Unable to create a new email Folder

Does it help to set mail.server.default.use_compress_deflate to false? (see https://support.mozilla.org/en-US/kb/config-editor)

OK, I found the problem cause. The new folder WAS created, but whereas it used to place it in alphabetical order, it added it at the very top. Since I have a LOT of folders, and the new one began with an S, I never noticed it as a new one at the very beginning. Normally, new folders have been slotted in the correct alphabetical order. Is this a bug?

How many folders at the same level? Is this a first level folder, immediately below the account?

First level which has 68 folders, 12 of which are after this folder.

There have been rare reports of new folders not being inserted alphabetically. But I have no useful information to resolve this.

Thanks. I have, on at least three occasions over the last two years, had some of my folders randomly moved out of order. I have four accounts, but can't recall if it happened in the same one. I just manually dragged them back in order.