tried to reproduce the error i mentioned, but doesn’t happen again – after rebuild & reboot of the whole box.
may have had something to do with files left in a weird state after simply restarting the app. have seen that in other cases here and on my own install as well. sorry for the noise 
@angus: the errors are back 
have been using your plugin a lot and i think switching to full-screen mode, either by me or who i have been chatting with, triggered the errors. when i did it my browser crashed as well (vivaldi-snapshot).
those CPU spikes were there too, but not as bad as they used to be. everything went back to normal quickly. probably because i slightly increased my droplet size and rebuilt the app, with more unicorn workers, etc.
attaching one of the backtraces as txt file, looks horrible in here.
here is the corresponding entry in
/var/discourse/shared/standalone/log/var-log/nginx/error.log
2018/06/09 17:49:52 [error] 306#306: *13863 open() "/var/www/discourse/public/assets/ember_jquery-27e777857b8c0730dacfe09cb11711365 d21a5db4f9ee0b85d494e4259cf6cda.js:2:16548" failed (2: No such file or directory), client: 13.57.114.123, server: _, request: "GET /assets/ember_jquery-27e777857b8c0730dacfe09cb11711365d21a5db4f9ee0b85d494e4259cf6cda.js:2:16548 HTTP/1.1", host: "discourse.mayapur-community.com"
i don’t see your plugin name mentioned in there, but even though i installed https://meta.discourse.org/t/focus-full-screen-composer-mode/85399 since then, the errors looked the same when they happened last time, w/o the focus-thing.
[edit: no. of error messages keeps increasing even w/o switching from quick to full page chat. but this doesn’t seem to have much of a negative effect on the site’s functioning anymore.]
error-backtrace.txt (1.5 KB)