Folders disappears and all mail lost

Hello,

I have a Dovecot 2.2.22 configured with mdbox storage.

THe server have about 50 mailboxes configured.

Only in one mailbox I have a strange problem, sometime (in the last 2 month happens 3 times).

All the mail (Except INBOX) and all folders disappear.

THe space on disk remain allocated.

To this mailbox are connected 3 computers (2 PC Windows 10, and 1 Mac OS).

I cannot determine who and why this happens to this mailbox.

Can someone tellme how I can find the PC that delete all mail.