Apple Mail: Duplicate Favourites folders won't delete

Apple Mail's Favorites has been giving me trouble for a long time and the problem has spanned several OS's (now Tahoe). When I mark a folder as a Favorite, it often appears twice in my Favorites list (but never together in the list). If I right click on the folder in the list, only one of the identical folders gives me the option to"Remove from favorites." When I remove one of them, the other one remains forever. I am afraid to delete the extra folder for fear of deleting all the contents of both folders (since they are actually the same folder). The only workaround that I have found is to create a brand new folder in my iCloud section with a slightly different name, then drag all the contents into the new folder and delete the original folder (both copies). This is a royal pain.

How can I prevent this from happening in the first place?