Not sure if this is the cause, but I'm seeing this in the logs

Nov 02 13:54:45 Caused by: Nov 02 13:54:45 NameError: uninitialized constant UserBookmarkBaseSerializer Nov 02 13:54:45 Did you mean? UserBookmarkListSerializer Nov 02 13:54:45 UserBookmarkSerializer

I really think the Discourse package needs some serious attention from @staff to ensure it can install and run all the official plugins.

So far 2/3 3/5 of the official plugins I've tried to install haven't worked (and 2/5 have completely bricked my install)