Gmail imap sync not working

Hi, i have a rather stange issue with my gmail account showing only the first one or two messages of my (probably rather big) inbox of my gmail account. However opening the folder list shows a correct number of mails i guess.

This error comes up hourly in the log:

Errormailvor einer Stunde

OCA\Mail\Exception\ServiceException: Sync failed for 2:[Gmail]/Alle Nachrichten: Error when communicating with the mail server.
/var/www/nextcloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php - line 107:

OCA\Mail\Service\Sync\ImapToDbSynchronizer->sync(OCA\Mail\Account {}, OCA\Mail\Db\Mailbox { id: 15}, 42, null, false)

/var/www/nextcloud/apps/mail/lib/BackgroundJob/SyncJob.php - line 92:

OCA\Mail\Service\Sync\ImapToDbSynchronizer->syncAccount(OCA\Mail\Account {})

/var/www/nextcloud/lib/public/BackgroundJob/Job.php - line 79:

OCA\Mail\BackgroundJob\SyncJob->run({ accountId: 2})

/var/www/nextcloud/lib/public/BackgroundJob/TimedJob.php - line 61:

OCP\BackgroundJob\Job->execute(OC\BackgroundJob\JobList {}, OC\Log {})

/var/www/nextcloud/cron.php - line 125:

OCP\BackgroundJob\TimedJob->execute(OC\BackgroundJob\JobList {}, OC\Log {})

Verursacht durchHorde_Imap_Client_Exception: Error when communicating with the mail server.
/var/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Socket.php - line 4542:

Horde_Imap_Client_Socket_Connection_Socket->read()

/var/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Socket.php - line 4314:

Horde_Imap_Client_Socket->_getLine(Horde_Imap_C … }})

/var/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Socket.php - line 4242:

Horde_Imap_Client_Socket->_sendCmdChunk(Horde_Imap_C … }}, [ Horde_Imap … }])

/var/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Socket.php - line 2476:

Horde_Imap_Client_Socket->_sendCmd(Horde_Imap_C … }})

/var/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Base.php - line 2267:

Horde_Imap_Client_Socket->_search(Horde_Imap_C … {}, { ids: Horde … }})

/var/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Data/Sync.php - line 223:

Horde_Imap_Client_Base->search(Horde_Imap_Client_Mailbox {}, Horde_Imap_C … {}, { ids: Horde … }})

/var/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Base.php - line 3634:

Horde_Imap_Client_Data_Sync->__construct(Horde_Imap_C … e}, Horde_Imap_Client_Mailbox {}, { U: "109414 … "}, { U: 109420, … 9}, 2, Horde_Imap_C … e})

/var/www/nextcloud/apps/mail/lib/IMAP/Sync/Synchronizer.php - line 62:

Horde_Imap_Client_Base->sync(Horde_Imap_Client_Mailbox {}, “U109414,V624956039,H2600422”, { criteria: … }})

/var/www/nextcloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php - line 311:

OCA\Mail\IMAP\Sync\Synchronizer->sync(Horde_Imap_C … e}, OCA\Mail\IMAP\Sync\Request {}, 2)

/var/www/nextcloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php - line 195:

OCA\Mail\Service\Sync\ImapToDbSynchronizer->runPartialSync(OCA\Mail\Account {}, OCA\Mail\Db\Mailbox { id: 15}, 42, null)

/var/www/nextcloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php - line 107:

OCA\Mail\Service\Sync\ImapToDbSynchronizer->sync(OCA\Mail\Account {}, OCA\Mail\Db\Mailbox { id: 15}, 42, null, false)

/var/www/nextcloud/apps/mail/lib/BackgroundJob/SyncJob.php - line 92:

OCA\Mail\Service\Sync\ImapToDbSynchronizer->syncAccount(OCA\Mail\Account {})

/var/www/nextcloud/lib/public/BackgroundJob/Job.php - line 79:

OCA\Mail\BackgroundJob\SyncJob->run({ accountId: 2})

/var/www/nextcloud/lib/public/BackgroundJob/TimedJob.php - line 61:

OCP\BackgroundJob\Job->execute(OC\BackgroundJob\JobList {}, OC\Log {})

/var/www/nextcloud/cron.php - line 125:

OCP\BackgroundJob\TimedJob->execute(OC\BackgroundJob\JobList {}, OC\Log {})