fwiw, I also recently had a few thousand points disappear, some in Aug & some in Sep?
Recent online activity revealed no transaction(s) deducting those points???
When I called in, I was told there was an audit of my account & supposedly @4 yrs ago they now say, I was awarded points on several award rentals???
I have no recollection of that and online activity records don't go back that far.
The CS rep also told me an email was sent, which of course was never received.
Not sure this is what happened to you but maybe it's worth another phone call?