Thanks Gavin. It did error out, but I restarted the upgrade, which was probably a mistake. Previously the upgrade bar below “Upgrade discourse” was moving until the error notification, but now nothing appears to be happening.
FWIW, my upgrade of the Docker Manager errored out a small while ago with the same “Sorry, there was an error upgrading Discourse…”, and I just pressed the blue Start Upgrading button again and the Docker Manager successfully updated the second time (though it was slow). I’m currently now updating Discourse itself, and it’s taking awhile too.
My test site has successfully updated now, though it did take longer than normal. My admin UI forces me to upgrade Docker Manager before it will let me ‘upgrade all’, so that probably helped.
My blue bar was moving, so I’m not sure I experienced the same stage as you’re getting at the minute. I’m afraid I didn’t time it, but I think the last ‘Update All’ took about 40 minutes, and the Docker Manager before that about the same?