Disappearing zone file

[Troy]

Does anyone have any idea why a zone file on a Plesk server would keep disappearing? We have one site where the dns zone simply vanishes, the site, naturally, stops responding, and the customer, naturally, gets upset. It happens daily, and I have no explanation why.

I can log into the control panel, access DNS for the domain, click Disable and Enable to recreate the file, and then everything is fine again for a few hours until it vanishes once again.