I see this kind of errors in the browser console:
I do not know if they are related errors but I share them, just in case…
a 502 error relative to the /push-service-worker.js
and 500 errors for the /admin/docker/upgrade
I tried to click on the start upgrading button when a plugin update had already begun to see what would happen → the upgrade seems to stop (the log disappears, after some minutes it reappears).
But If I click to turn back to the docker/upgrade/versions I see this:
and if I click on Currently Upgrading:
I can see the disappeared buttons (the log reappears after few minutes, about 3 or 4, at the beginning it remains completely empty).