>>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.

Googling [identity theft bill diversion] yields lots of hits.