Emails deleting on their own

Lately it has happened a few times that all of a sudden mails are being deleted in my inbox, one after the other.

I see the mails being deleted, and cannot stop it, only by closing em client.

Is this a known issue?

Is auto archiving after xx days activated ? (settings)

Yes, but if it happens before a backup was made I lose all emails that were not archived yet.

Is this a known issue?

Do you use imap or exchange for connecting? Maybe there is a rule for deleting, or other user deleted the mails.