My locks are misbehaving

The electric locks on my 2005 Prius aren't working right. When I press the button on the door or press the button on the fob, I hear the locks engage twice and I don't get the beep and the lights don't flash. It still beeps and flashes the lights when I unlock.

I tried it with my wife's Prius and her locks only engage once (and it beeps).

It seems like it doesn't believe that it sucessfully locked the car, but I've tested it and all the doors are indeed locked.

I've noticed over the past couple of weeks that sometimes the beep was delayed. I would push the button, start to walk away, realize I didn't hear the beep, and then the beep would go off. I thought it was an issue with the battery in my fob and it was just taking longer to recognize that my fob was near, but I think now it simply sometimes didn't think it was successful in locked until after the second attempt, therefore causing the delay. But now it never beeps.

I tried opening and closing all the doors and hatch, and toggling the door locks in case one of the locks was partially engaged, but no luck.

Has anyone else had this problem?