I also ran into this problem.
The sidekiq dashboard showed nothing active, all five job slots were filled with 21-hour-old jobs, so sidekiq wasn’t pulling any new jobs of any sort, and the enqueued count was growing. I needed to apply system updates anyway, so I just restarted the system, which fixed the the problem.
The who’s online queue growing was my first tip-off.
Visiting the sidekiq dashboard did not “give it a kick”
Additionally, I noticed this warning on the Discourse dashboard:
I’m wondering whether that meant that there’s a warning that just didn’t show in the UI somewhere. I didn’t notice that warning immediately after my last update, to 176ee0bf60. I don’t check the dashboard often enough to know when it would have shown up.