Since iOS 18.1, no longer able to see Mail subfolders.

iOS 18.1 on an iPhone 15 Pro Max.

Self-hosted email, Debian 12, Dovecot 2.3.19.1 (9b53102964)

No changes to mail server. This has worked without issue for years and years. Standard IMAP/SSL setup.

Folders ARE VISIBLE with Mac OS Sequoia 15.1 Mail.

I can create/view/delete folders in Sequoia with no problems.

Folders also visible from webmail.

Folders NO LONGER visible on iOS 18.1, although if I choose "Move Message," I CAN see the folders, and I CAN move email. The email will show up as expected if I view with macOS Mail.

"Delete & Recreate account" DID NOT SOLVE.

Reboot iPhone DID NOT SOLVE.

I am sysadmin on mail server, I enabled debug and there were NO errors on the mail server side at all. Mail folder structure is valid:

drwx------  5 vmail vmail 4.0K Oct 31 17:55  .Sent/
drwx------  5 vmail vmail 4.0K Jun 22 12:27  .Storage/
drwx------  5 vmail vmail 4.0K Oct  1 23:52  .Storage.2023/
drwx------  5 vmail vmail 4.0K Oct 31 17:48  .Storage.2024/

I am able to see items in "Sent" without problems, but nothing in Storage or the subfolders.

I am not seeing the POSIX error that others are, but I cannot see subfolders that other mail clients can see.