There was indeed a bug… The query that was “listing” all the chat users with unread mentions or DMs was not quite working and was returning all the users with unseen chat messages 
Since that job runs every 5 minutes, it can easily bloat sidekiq with unnecessary jobs on large channels with a fair amount of activity.
Thankfully it wasn’t spamming everyone as the “chat summary” job was extracting the unseen mentions and when it found none, just bailed out.
Will be fixed by