Sometimes (especially in the later game when there is a lot going on), I'll put an item in a production queue for a planet and it will be removed from that planet's queue when the next turn starts. One time it was 15x civil transports; another time it was a pollution processor.

In either case, the planet seems to "remember" how it as faring on the project - if I again put that item into the production queue, it retains the work on it that was done that turn. Each turn it will remove it again, and each turn I can put it back in the queue and slowly get it closer to completion. However, when it comes time for the project to finish, it removes it from the queue and never completes. It doesn't matter if it is the only item in the queue or if there are other projects in line behind it, and it doesn't matter how many times I push it back into the queue - it forever sits at 1 turn left to completion and never completes.

Anyone seen this bug and have a work-around? (Assuming, of course, that the developers are finished updating/patching this game and that I should not expect further official bug fixes.)

Hmm...I'm using the "LOCFIX (GOG)" patch, 55.1.1.2.1.41258. I'm afraid I'm not entirely sure what "UCP" is, nor whether my patch is more recent than the one you mention, but I'm encountering the problem in new games (as of a week ago), so I imagine mine is older.

EDIT: Ah, "unofficial code patch," and I see I have to install and run it as a mod. Is that correct?

Yep Unofficial Code Patch: https://www.nexusmods.com/masteroforionconquerthestars/mods/30

Otherwise if you do not want or cannot run that (OSX GOG version) then I would recommend not building in bulk to avoid this issue.

Unfortunately I am using the GOG OSX version. Thanks, though, for all your work on this patch.