This may be silly and you have all thought of it, but...
After reading through this thread and having had the issue myself a bit, I thought about how the handle works and realized I was doing it to myself.
When you go to unlock the vehicle, you just put your fingers around the handle and it unlocks. What I didn't think through at first was if you put your fingers in the handle when you press the lock button, the handle is being asked to both unlock and lock the vehicle at the same time.
So, starting Saturday up to and including today, I have been careful to just press the button without putting my fingers into the handle, and so far, it has locked every time.
Hope this helps at least someone