Hi all - I'm running Thunderbird (14.05) on a desktop Mac running Sequoia 15.7.2

In my Local Folders, I have sub folders which in turn have a large number of subfolders. All of those sub folders are automatically listed alphabetically as they're created. In the last couple days, a fairly random selection of six folders from topline folders, sub folders and subsub folders have been shifted to the end of the alphabetized list and I have absolutely no idea why. I can manually move them back no problem, but I'd really like to stop it happening again! Also, I've tried clicking on the topline folder and choosing to sort by subject, but it changes nothing. Even renaming an mis-listed folder to a new name does not make it move to its correct place in the alphabet. Any ideas? Thanks