>Seriously:
>
>1. Identity theft. Crooks may divert bills for non-financial reasons e.g. use as credentials to access your health care provider etc. I'd get on this real fast.
>
>2. Have the automatic payments been switched to some other account you're not monitoring?
>
>3. Do you have any kind of automatic transfers set up between various accounts?


The automatic payment wasn't switched. Yes, there are automatic transfers between accounts, though they were set up a long time ago.

I've tried to figure out what else changed during this time, and so far can't think of any.

The identify theft definitely concerns me. About two years ago I had my credit card info breached and had to get a new card, but this is much stranger.