IMAP/office365 issues (double ticket and interpreter error)

Lately, our imap piping is working very slow with many memory in use (700+ MB).

Also, tickets are not interpreted well

(QmVzdGUgQmxhYQ0KDQpCbGFhDQpKZGthbA0KDQpKZGhqdXFob3ENCg0KZGphc2sNCg=) instead readable text.

Thirdly: our emails are converted as tickets twice (both the same email, but it hasn't been moved to Archive for some reason)

The problem existed with version 4.2 (on php7.2-fpm) and version 4.3 (on php7.2-fpm and php7.4-fpm)
We are using Office365 with IMAP support
Our ticket system has approx 718 tickets and 1025 replies
Has worked perfectly since december 2019 till last week
We have a paid license to Maian support.

On 4.2/php7.2 we also experienced this:

[Wed Jan 20 10:54:20.284492 2021] [proxy_fcgi:error] [pid 7847:tid 140044136191744] [client 185.103.159.154:37720] AH01071: Got error 'PHP message: PHP Fatal error:  Out of memory (allocated 378564608) (tried to allocate 376465528 bytes) in /home/**userremoved**/domains/dtc.**domainremoved**.net/public_html/control/classes/class.imap.php on line 533\nPHP message: PHP Fatal error:  Uncaught Error: Call to undefined function linending() in /home/**userremoved**/domains/dtc.**domainremoved**.net/public_html/control/classes/class.errors.php:54\nStack trace:\n#0 [internal function]: msFatalErr()\n#1 {main}\n  thrown in /home/**userremoved**/domains/dtc.**domainremoved**.net/public_html/control/classes/class.errors.php on line 54\n'

Anybody a clue?