Found the cause.
Possibly restarting the Zammad service is good enough already.
Your logfile and description do not fit.
Your production log shows a running scheduler and functioning fetch process.
If mails are vanshing from your mailbox but not appearing on your Zammad instance ensure the following:
!!!* no other Zammad instance fetching mail from the same mailbox!!!
- you having enough permissions to see the group the ticket may be directed to
MrGeneration Thank you