MailboxDoesNotSupportModSequencesException problem with mails

Expected behavior

Mail app shall load mails

Actual behavior

Mail app load mails, mails disappears some seconds later, then some seconds later they appear again - endless loop of appearance, disappearance

This pull request seems to be expected to fix the issue:
https://github.com/nextcloud/mail/pull/3560
but it does not. I checked ImapToDbSynchronizer.php and it contains this non working fix

Mail app

Mail app version:
1.8.1

Mailserver or service: (e.g. Outlook, Yahoo, Gmail, Exchange,...)
mail.manitu.de
OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN AUTH=LOGIN] Dovecot ready

Server configuration

Operating system: (e.g. Debian 8)
Gentoo Linux (Kernel 5.4.89)

Web server: (e.g. Apache, Nginx,...)
Apache

Database: (e.g. MariaDB, SQLite or PostgreSQL)
MySQL 8

PHP version: (e.g. 7.0)
PHP 7.3

Nextcloud Version: (see admin page, e.g. 13.0.2)
20.0.7

Client configuration

Browser: (e.g. Firefox 48)
Firefox 85

Operating system: (e.g. Arch Linux)
Windows

Stack

OCA\Mail\Exception\MailboxDoesNotSupportModSequencesException: Mailbox does not support mod-sequences.
/var/www/cloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php - line 399:
OCA\Mail\IMAP\Sync\Synchronizer->sync()
/var/www/cloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php - line 221:
OCA\Mail\Service\Sync\ImapToDbSynchronizer->runPartialSync()
/var/www/cloud/apps/mail/lib/Service/Sync/SyncService.php - line 121:
OCA\Mail\Service\Sync\ImapToDbSynchronizer->sync()
/var/www/cloud/apps/mail/lib/Controller/MailboxesController.php - line 161:
OCA\Mail\Service\Sync\SyncService->syncMailbox()
/var/www/cloud/lib/private/AppFramework/Http/Dispatcher.php - line 169:
OCA\Mail\Controller\MailboxesController->sync()
/var/www/cloud/lib/private/AppFramework/Http/Dispatcher.php - line 100:
OC\AppFramework\Http\Dispatcher->executeController()
/var/www/cloud/lib/private/AppFramework/App.php - line 152:
OC\AppFramework\Http\Dispatcher->dispatch()
/var/www/cloud/lib/private/Route/Router.php - line 309:
OC\AppFramework\App::main()
/var/www/cloud/lib/base.php - line 1008:
OC\Route\Router->match()
/var/www/cloud/index.php - line 37:
OC::handleRequest()
Verursacht durchHorde_Imap_Client_Exception: Mailbox does not support mod-sequences.
/var/www/cloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Data/Sync.php - line 244:
Horde_Imap_Client_Base->vanished()
/var/www/cloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Base.php - line 3634:
Horde_Imap_Client_Data_Sync->__construct()
/var/www/cloud/apps/mail/lib/IMAP/Sync/Synchronizer.php - line 151:
Horde_Imap_Client_Base->sync()
<>
OCA\Mail\IMAP\Sync\Synchronizer->OCA\Mail\IMAP\Sync{closure}("*** sensiti ... *")
/var/www/cloud/apps/mail/lib/IMAP/Sync/Synchronizer.php - line 154:
array_map()
/var/www/cloud/apps/mail/lib/IMAP/Sync/Synchronizer.php - line 75:
OCA\Mail\IMAP\Sync\Synchronizer->getVanishedMessageUids()
/var/www/cloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php - line 399:
OCA\Mail\IMAP\Sync\Synchronizer->sync()
/var/www/cloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php - line 221:
OCA\Mail\Service\Sync\ImapToDbSynchronizer->runPartialSync()
/var/www/cloud/apps/mail/lib/Service/Sync/SyncService.php - line 121:
OCA\Mail\Service\Sync\ImapToDbSynchronizer->sync()
/var/www/cloud/apps/mail/lib/Controller/MailboxesController.php - line 161:
OCA\Mail\Service\Sync\SyncService->syncMailbox()
/var/www/cloud/lib/private/AppFramework/Http/Dispatcher.php - line 169:
OCA\Mail\Controller\MailboxesController->sync()
/var/www/cloud/lib/private/AppFramework/Http/Dispatcher.php - line 100:
OC\AppFramework\Http\Dispatcher->executeController()
/var/www/cloud/lib/private/AppFramework/App.php - line 152:
OC\AppFramework\Http\Dispatcher->dispatch()
/var/www/cloud/lib/private/Route/Router.php - line 309:
OC\AppFramework\App::main()
/var/www/cloud/lib/base.php - line 1008:
OC\Route\Router->match()
/var/www/cloud/index.php - line 37:
OC::handleRequest()

Start with lib/Service/Sync/ImapToDbSynchronizer.php around lines 221 and 399, then trace the call into lib/IMAP/Sync/Synchronizer.php and Horde_Imap_Client_Data_Sync in the stack trace. Compare the existing behavior with pull request 3560 and determine why a mailbox without mod-sequences repeatedly fails synchronization. Done means the mailbox loads without the disappearance/reappearance loop or recurring exception.