さて、もう確信が持てなくなってきました。
Fingerprint を無効にしてもログには依然として大量のエラーが発生しており、通常モードでは新しいユーザーを作成できません。セーフモードでは新しいユーザーを作成できたので、もしかするとテーマコンポーネントの問題かもしれません。
10 分以内に、以下の 3 つのバックトレースそれぞれについて 10 件のエラーが発生しました。
1:
メッセージ（10 件のコピーが報告されました）
ジョブ例外：スレッドを割り当てできません
バックトレース
/usr/local/lib/ruby/3.4.0/socket.rb:712:in 'Thread.new'
/usr/local/lib/ruby/3.4.0/socket.rb:712:in 'block in Socket.tcp_with_fast_fallback'
/usr/local/lib/ruby/3.4.0/socket.rb:710:in 'Array#map'
/usr/local/lib/ruby/3.4.0/socket.rb:710:in 'Socket.tcp_with_fast_fallback'
/usr/local/lib/ruby/3.4.0/socket.rb:661:in 'Socket.tcp'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client/ruby_connection.rb:122:in 'RedisClient::RubyConnection#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client/ruby_connection.rb:48:in 'RedisClient::RubyConnection#initialize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:815:in 'Class#new'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:815:in 'block in RedisClient#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client/middlewares.rb:12:in 'RedisClient::BasicMiddleware#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:814:in 'RedisClient#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:800:in 'RedisClient#raw_connection'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:759:in 'RedisClient#ensure_connected'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:352:in 'RedisClient#call_v'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis/client.rb:90:in 'Redis::Client#call_v'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/rack-mini-profiler-4.0.1/lib/mini_profiler/profiling_methods.rb:90:in 'block in Redis::Client#profile_method'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis.rb:152:in 'block in Redis#send_command'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis.rb:151:in 'Monitor#synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis.rb:151:in 'Redis#send_command'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis/commands/keys.rb:280:in 'Redis::Commands::Keys#exists?'
/var/www/discourse/lib/discourse_redis.rb:156:in 'block in DiscourseRedis#exists?'
/var/www/discourse/lib/discourse_redis.rb:29:in 'DiscourseRedis.ignore_readonly'
/var/www/discourse/lib/discourse_redis.rb:156:in 'DiscourseRedis#exists?'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:303:in 'MiniScheduler::Manager#repair_queue'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:46:in 'MiniScheduler::Manager::Runner#repair_queue'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:21:in 'block (2 levels) in MiniScheduler::Manager::Runner#initialize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:20:in 'Thread::Mutex#synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:20:in 'block in MiniScheduler::Manager::Runner#initialize'
2:
メッセージ（10 件のコピーが報告されました）
ジョブ例外：スレッドを割り当てできません
バックトレース
/usr/local/lib/ruby/3.4.0/socket.rb:712:in 'Thread.new'
/usr/local/lib/ruby/3.4.0/socket.rb:712:in 'block in Socket.tcp_with_fast_fallback'
/usr/local/lib/ruby/3.4.0/socket.rb:710:in 'Array#map'
/usr/local/lib/ruby/3.4.0/socket.rb:710:in 'Socket.tcp_with_fast_fallback'
/usr/local/lib/ruby/3.4.0/socket.rb:661:in 'Socket.tcp'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client/ruby_connection.rb:122:in 'RedisClient::RubyConnection#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client/ruby_connection.rb:48:in 'RedisClient::RubyConnection#initialize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:815:in 'Class#new'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:815:in 'block in RedisClient#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client/middlewares.rb:12:in 'RedisClient::BasicMiddleware#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:814:in 'RedisClient#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:800:in 'RedisClient#raw_connection'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:759:in 'RedisClient#ensure_connected'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:352:in 'RedisClient#call_v'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis/client.rb:90:in 'Redis::Client#call_v'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/rack-mini-profiler-4.0.1/lib/mini_profiler/profiling_methods.rb:90:in 'block in Redis::Client#profile_method'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis.rb:152:in 'block in Redis#send_command'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis.rb:151:in 'Monitor#synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis.rb:151:in 'Redis#send_command'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis/commands/keys.rb:256:in 'Redis::Commands::Keys#del'
/var/www/discourse/lib/discourse_redis.rb:168:in 'block in DiscourseRedis#del'
/var/www/discourse/lib/discourse_redis.rb:29:in 'DiscourseRedis.ignore_readonly'
/var/www/discourse/lib/discourse_redis.rb:165:in 'DiscourseRedis#del'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/distributed_mutex.rb:48:in 'MiniScheduler::DistributedMutex#synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/distributed_mutex.rb:15:in 'MiniScheduler::DistributedMutex.synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:365:in 'MiniScheduler::Manager#lock'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:273:in 'MiniScheduler::Manager#reschedule_orphans!'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:52:in 'MiniScheduler::Manager::Runner#reschedule_orphans'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:22:in 'block (2 levels) in MiniScheduler::Manager::Runner#initialize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:20:in 'Thread::Mutex#synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:20:in 'block in MiniScheduler::Manager::Runner#initialize'
3:
メッセージ（10 件のコピーが報告されました）
ジョブ例外：スレッドを割り当てできません
バックトレース
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:63:in 'Thread.new'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:63:in 'block in MiniScheduler::Manager::Runner#ensure_worker_threads'
<internal:numeric>:257:in 'Integer#times'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:63:in 'MiniScheduler::Manager::Runner#ensure_worker_threads'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:23:in 'block (2 levels) in MiniScheduler::Manager::Runner#initialize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:20:in 'Thread::Mutex#synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:20:in 'block in MiniScheduler::Manager::Runner#initialize'
また、10 分以内にこのエラーが 585 件発生しました。
メッセージ（585 件のコピーが報告されました）
ジョブ例外：スレッドを割り当てできません
バックトレース
/usr/local/lib/ruby/3.4.0/socket.rb:712:in 'Thread.new'
/usr/local/lib/ruby/3.4.0/socket.rb:712:in 'block in Socket.tcp_with_fast_fallback'
/usr/local/lib/ruby/3.4.0/socket.rb:710:in 'Array#map'
/usr/local/lib/ruby/3.4.0/socket.rb:710:in 'Socket.tcp_with_fast_fallback'
/usr/local/lib/ruby/3.4.0/socket.rb:661:in 'Socket.tcp'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client/ruby_connection.rb:122:in 'RedisClient::RubyConnection#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client/ruby_connection.rb:48:in 'RedisClient::RubyConnection#initialize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:815:in 'Class#new'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:815:in 'block in RedisClient#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client/middlewares.rb:12:in 'RedisClient::BasicMiddleware#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:814:in 'RedisClient#connect'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:800:in 'RedisClient#raw_connection'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:759:in 'RedisClient#ensure_connected'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-client-0.26.1/lib/redis_client.rb:352:in 'RedisClient#call_v'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis/client.rb:90:in 'Redis::Client#call_v'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/rack-mini-profiler-4.0.1/lib/mini_profiler/profiling_methods.rb:90:in 'block in Redis::Client#profile_method'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis.rb:152:in 'block in Redis#send_command'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis.rb:151:in 'Monitor#synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis.rb:151:in 'Redis#send_command'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/redis-5.4.0/lib/redis/commands/keys.rb:256:in 'Redis::Commands::Keys#del'
/var/www/discourse/lib/discourse_redis.rb:168:in 'block in DiscourseRedis#del'
/var/www/discourse/lib/discourse_redis.rb:29:in 'DiscourseRedis.ignore_readonly'
/var/www/discourse/lib/discourse_redis.rb:165:in 'DiscourseRedis#del'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/distributed_mutex.rb:48:in 'MiniScheduler::DistributedMutex#synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/distributed_mutex.rb:15:in 'MiniScheduler::DistributedMutex.synchronize'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:365:in 'MiniScheduler::Manager#lock'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler/manager.rb:316:in 'MiniScheduler::Manager#tick'
/var/www/discourse/vendor/bundle/ruby/3.4.0/gems/mini_scheduler-0.18.0/lib/mini_scheduler.rb:74:in 'block (2 levels) in MiniScheduler.start'
コアプラグイン以外でインストールしているのは、Fingerprint（現在は無効化）、Staff Alias、および Always-Anonymous Categories Plugin のみです。他の有効なプラグインはすべてコア由来のものです。
私のテーマコンポーネントは以下の通りです。
- Category banners
- Clickable topics
- Colorful categories
- Avatar size and shape
- Favorite Filters
- Fingerprint button
- Progress Bar
- Sidebar theme toggle
- Tag banners
- Topic list excerpt
- コoked 要素を装飾する小さなカスタムテーマコンポーネント
テーマコンポーネントを一つずつ無効化して確認するべきでしょうか？ログインプロセスに影響を与える可能性があるとは思えないものしかインストールしていませんが。