idb file randomly being deleted/going missing - how to troubleshoot?

Full disclosure, I'm a website owner, not a professional DBA. I hope this question is OK. I'm trying to discover why an idb file is, seemingly randomly at a rate of around once every 4-7 days, disappearing from our web server (the associated frm file remains intact). This file is related to a well-supported Wordpress plugin but we seem to be the only user affected by this issue. Unfortunately I see nothing in the mysql error logs and neither the plugin developer nor our web host can explain what's going on. Is there any auditing/logging I can enable to give me some clue as to why this may be happening? We're running MySQL Version 10.6.14-MariaDB. Many thanks.