Ford goes retiree

I have an '01 Ford Explorer Sport-Trac that has a quirk. Whenever the outside temp goes below about 60 or so, the driver’s door lock will not work–either with the key fob, the keypad, or the button. Warmer temps, everything works fine, and all of the other doors work fine all of the time. Any thoughts on this phenomenon?

Old grease and oils thicken and harden, even more in the cold.
I would pull the inner door panel and spray some silicone lubricant in the mechanism.

I agree. Ever watch power widows operate in 20 degree weather? They slow down considerably.

Had this done at the shop. When you insert the key, the lock opens easily and freely. Again, all the other doors work. Could this be a security system issue?