"Waiting for unicorn to reload", then update stops

Unfortunately I still see the exact same issue as described above. CLI rebuild works fine, UI upgrade consistently fails. I am currently on commit 577af81 from December 17.

Stack trace
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*** Please be patient, next steps might take a while ***
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Cycling Unicorn, to free up memory
Restarting unicorn pid: 43
Waiting for Unicorn to reload.
Waiting for Unicorn to reload..
Waiting for Unicorn to reload...
Waiting for Unicorn to reload....
Waiting for Unicorn to reload.....
Waiting for Unicorn to reload......
Waiting for Unicorn to reload.......
Waiting for Unicorn to reload........
Waiting for Unicorn to reload.........
Waiting for Unicorn to reload..........
Waiting for Unicorn to reload...........
Waiting for Unicorn to reload............
Waiting for Unicorn to reload.............
Waiting for Unicorn to reload..............
Waiting for Unicorn to reload...............
Waiting for Unicorn to reload................
Waiting for Unicorn to reload.................
Waiting for Unicorn to reload..................
Waiting for Unicorn to reload...................
Waiting for Unicorn to reload....................
Waiting for Unicorn to reload.....................
Waiting for Unicorn to reload......................
Waiting for Unicorn to reload.......................
Waiting for Unicorn to reload........................
Waiting for Unicorn to reload.........................
Waiting for Unicorn to reload..........................
Waiting for Unicorn to reload...........................
Waiting for Unicorn to reload............................
Waiting for Unicorn to reload.............................
Waiting for Unicorn to reload..............................
Waiting for Unicorn to reload...............................
Waiting for Unicorn to reload................................
Waiting for Unicorn to reload.................................
Waiting for Unicorn to reload..................................
Waiting for Unicorn to reload...................................
Waiting for Unicorn to reload....................................
Waiting for Unicorn to reload.....................................
Waiting for Unicorn to reload......................................
Waiting for Unicorn to reload.......................................
Waiting for Unicorn to reload........................................
Waiting for Unicorn to reload.........................................
Waiting for Unicorn to reload..........................................
Waiting for Unicorn to reload...........................................
Waiting for Unicorn to reload............................................
Waiting for Unicorn to reload.............................................
Waiting for Unicorn to reload..............................................
Waiting for Unicorn to reload...............................................
Waiting for Unicorn to reload................................................
Waiting for Unicorn to reload.................................................
Waiting for Unicorn to reload..................................................
Waiting for Unicorn to reload...................................................
Waiting for Unicorn to reload....................................................
Waiting for Unicorn to reload.....................................................
Waiting for Unicorn to reload......................................................
Waiting for Unicorn to reload.......................................................
Waiting for Unicorn to reload........................................................
Waiting for Unicorn to reload.........................................................
Waiting for Unicorn to reload..........................................................
Waiting for Unicorn to reload...........................................................
Stopping 1 Unicorn worker(s), to free up memory
Stopping job queue to reclaim memory, master pid is 28696
Docker Manager: FAILED TO UPGRADE
#<Errno::ESRCH: No such process>
/var/www/discourse/lib/demon/base.rb:71:in `kill'
/var/www/discourse/lib/demon/base.rb:71:in `stop'
/var/www/discourse/lib/demon/base.rb:20:in `block in stop'
/var/www/discourse/lib/demon/base.rb:19:in `each'
/var/www/discourse/lib/demon/base.rb:19:in `stop'
config/unicorn.conf.rb:136:in `block (2 levels) in reload'
/var/www/discourse/plugins/docker_manager/lib/docker_manager/upgrader.rb:60:in `kill'
/var/www/discourse/plugins/docker_manager/lib/docker_manager/upgrader.rb:60:in `upgrade'
/var/www/discourse/plugins/docker_manager/app/controllers/docker_manager/admin_controller.rb:91:in `block in upgrade'
/var/www/discourse/plugins/docker_manager/app/controllers/docker_manager/admin_controller.rb:87:in `fork'
/var/www/discourse/plugins/docker_manager/app/controllers/docker_manager/admin_controller.rb:87:in `upgrade'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/basic_implicit_render.rb:6:in `send_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/abstract_controller/base.rb:194:in `process_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/rendering.rb:30:in `process_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/abstract_controller/callbacks.rb:42:in `block in process_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/callbacks.rb:132:in `run_callbacks'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/abstract_controller/callbacks.rb:41:in `process_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/rescue.rb:22:in `process_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/instrumentation.rb:34:in `block in process_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/notifications.rb:168:in `block in instrument'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/notifications/instrumenter.rb:23:in `instrument'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/notifications.rb:168:in `instrument'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/instrumentation.rb:32:in `process_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/params_wrapper.rb:256:in `process_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/activerecord-5.2.2/lib/active_record/railties/controller_runtime.rb:24:in `process_action'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/abstract_controller/base.rb:134:in `process'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionview-5.2.2/lib/action_view/rendering.rb:32:in `process'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-mini-profiler-1.0.1/lib/mini_profiler/profiling_methods.rb:78:in `block in profile_method'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal.rb:191:in `dispatch'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal.rb:252:in `dispatch'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/route_set.rb:52:in `dispatch'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/route_set.rb:34:in `serve'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/mapper.rb:18:in `block in <class:Constraints>'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/mapper.rb:48:in `serve'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/journey/router.rb:52:in `block in serve'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/journey/router.rb:35:in `each'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/journey/router.rb:35:in `serve'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/route_set.rb:840:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/railties-5.2.2/lib/rails/engine.rb:524:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/railties-5.2.2/lib/rails/railtie.rb:190:in `public_send'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/railties-5.2.2/lib/rails/railtie.rb:190:in `method_missing'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/mapper.rb:19:in `block in <class:Constraints>'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/mapper.rb:48:in `serve'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/journey/router.rb:52:in `block in serve'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/journey/router.rb:35:in `each'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/journey/router.rb:35:in `serve'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/route_set.rb:840:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-protection-2.0.3/lib/rack/protection/frame_options.rb:31:in `call'
/var/www/discourse/lib/middleware/omniauth_bypass_middleware.rb:32:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/tempfile_reaper.rb:15:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/conditional_get.rb:38:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/head.rb:12:in `call'
/var/www/discourse/lib/content_security_policy/middleware.rb:12:in `call'
/var/www/discourse/lib/middleware/anonymous_cache.rb:216:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/session/abstract/id.rb:232:in `context'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/session/abstract/id.rb:226:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/cookies.rb:670:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/callbacks.rb:98:in `run_callbacks'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/callbacks.rb:26:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/debug_exceptions.rb:61:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/logster-1.3.1/lib/logster/middleware/reporter.rb:31:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/railties-5.2.2/lib/rails/rack/logger.rb:38:in `call_app'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/railties-5.2.2/lib/rails/rack/logger.rb:28:in `call'
/var/www/discourse/config/initializers/100-quiet_logger.rb:16:in `call'
/var/www/discourse/config/initializers/100-silence_logger.rb:29:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/remote_ip.rb:81:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/request_id.rb:27:in `call'
/var/www/discourse/lib/middleware/enforce_hostname.rb:17:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/method_override.rb:22:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/executor.rb:14:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/sendfile.rb:111:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-mini-profiler-1.0.1/lib/mini_profiler/profiler.rb:171:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/message_bus-2.2.0.pre.1/lib/message_bus/rack/middleware.rb:57:in `call'
/var/www/discourse/lib/middleware/request_tracker.rb:180:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/railties-5.2.2/lib/rails/engine.rb:524:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/railties-5.2.2/lib/rails/railtie.rb:190:in `public_send'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/railties-5.2.2/lib/rails/railtie.rb:190:in `method_missing'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/urlmap.rb:68:in `block in call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/urlmap.rb:53:in `each'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-2.0.6/lib/rack/urlmap.rb:53:in `call'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/unicorn-5.4.0/lib/unicorn/http_server.rb:606:in `process_client'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/unicorn-5.4.0/lib/unicorn/http_server.rb:701:in `worker_loop'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/unicorn-5.4.0/lib/unicorn/http_server.rb:549:in `spawn_missing_workers'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/unicorn-5.4.0/lib/unicorn/http_server.rb:142:in `start'
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/unicorn-5.4.0/bin/unicorn:126:in `<top (required)>'
/var/www/discourse/vendor/bundle/ruby/2.5.0/bin/unicorn:23:in `load'
/var/www/discourse/vendor/bundle/ruby/2.5.0/bin/unicorn:23:in `<main>'
Spinning up 1 Unicorn worker(s) that were stopped initially