Another door (un)lock problem

I did a search first and read through other posts about door lock problems, but haven't found someone with the same problems. I don't have problems with interior lights, windshield washers, or the trunk lid. The car doesn't have an alarm or remote start. I'm the original owner so I'm familiar with the work done on the car.
The doors have issues (un)locking in hot weather or when sitting out under the sun for awhile in the southern U.S. When I say problems (un)locking, that includes using the key fob, key in door handle, central button, and inside door handles.
If I walk up to the car & hit the unlock button, there is a sound like the doors unlock but none of the door locks pop up on any of the doors. Then, I stick the key into either front door, and sometimes I have luck getting the lock to come up enough to get the door open. Other times, I just have to wait a couple hours and try again.
Once inside, pulling the inside door handle on ANY of the doors doesn't cause them to unlock and open. Pushing the central (un)lock button doesn't make a noise or cause anything to (un)lock. Beating my head on the steering wheel didn't fix the problem. :banghead:
The door locks start working after starting the car and letting it run for a few minutes.
I haven't tried rolling down the windows while this is happening because I've been focused on getting the passenger side door open so my wife can get in. The problem doesn't happen regularly though, so I can't predict when it will happen. This really hampers troubleshooting. The weather is in the 70's and everything (key fob & locks) is working fine.

Any suggestions? Thanks.