Hello @Joojooba thank you for your post about this achievement issue.
I can confirm that this issue was known to us after the last update and regretabbly, this is not something we are able to fix, we do not have the ability to retroactively reset these achievements for the other DLC's back to an unattained status.
For your convenience, here is the Anno Union blog update from the dev's, where they mention this >
'Starting with some bad news, but it’s something we have seen multiple comments about recently: We have investigated the issue with Anno 1800’s achievements having been unlocked for some players at the beginning of September during the technical issues with Ubisoft Connect. Unfortunately, this issue cannot be fixed retroactively, and we are not able to reset your achievement progress.'