Harold- your freezer door has ESP (Error Some Place). The thumb-activated pin is sprung to return upward and spring-load the ball into the "hole" of the keyhole, so you have to press w/your thumb to release the ball to open the door. Sounds like a matter of adjustment to achieve a positive locking.
I'm guessing either the door isn't shutting all the way so the ball doesn't get "caught" in the keyhole, something in the thumb-pad-to-pin assembly has shifted so the ball rides too low to catch, or the keyhole casting is broken. First I'd check all around the door for obstructions to a fully closed condition. Second check to see that the lower face of keyhole consists of cast-plastic ribs making a ramp for the ball to ride on and to lock against once in the hole; maybe those ribs have broken off (maybe somebody yanked it open in frustration to get the Chunky Monkey?). Last resort, take the door apart.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project