@sa2000: well, the library is big enough to not consider it as small, I guess 
8192 matches [Notify] Now watching ... 3400 matches [Notify] Failed to add watch for ...
Seems like 8292 is the hard limit. Though a clean 3400 failed does look somehow suspicous as well.
Hontestly, as those entries have the log level DEBUNG and start with “Notifify”, i didn’t realy bothered making sense of those lines.
Seems like https://forums.plex.tv/discussion/comment/1409740/#Comment_1409740 is the fix.
update:
Following the suggested fix, did the trick 
Add fs.inotify.max_user_watches=100000 to /etc/sysctl.conf.
Reload config changes with sysctl --system
@sa2000: Thanks for pointing in the right direction!
