Unfortunately, this bug has been here for years. You're right that it seems to occur when switching aspirations and could technically be completed as long as one never switches. Super annoying since it's exactly the kind of aspiration you'd want to switch regularly. Hopefully Ea will fix it soon (which seems extremely unlikely at this point due to how much time has passed). Feel free to complain to Ea some more to try and draw more attention to it. In the meantime, I believe that there's a cheat that allows one to complete aspiration milestones but I'm not familiar with it and don't use it because cheats disable achievements on my Xbox.
I haven't switched aspirations. Went all the way through to day fourteen of the final Milestone (don't drink without permission for 14 days) and it rolled back to zero. He was at work when it happened so I don't know if that has a bearing.
I've put a lot of time into this household and don't want to resort to cheats so I'm just gong to mentally mark this down as complete and move on to another family...
