lone frozen keg

ihave read previous threads about frozen kegs and i know that my beer is ok, but i cant figure this one out. I have 3 kegs in the fridge and turn down the temp 38 because wife needed lagering fridge for 2 days and i'm trying to use one fridge for serving and lagering. one keg (rye wheat with the highest carbonation and some particulate hops) froze. 2 other kegs didnt freeze(marzen and honey blonde) and neither did any of the bottled beer. thermometer in fridge reads about 40. i'm not worried but i'm missing the logic here.

Possibly position in the fridge. Maybe it's real close to the coils? Also, my kegerator leaks from the freezer. The pool at the bottom of my fridge freezes when I set my CO2 tank in it.

Probably position. In my old kegger the evaporator was on the back wall and the back kegs would be 5-7F colder than the front ones. This did have some pluses.

thanks. as usual the simplest answer is usually correct. next time i need to lager in this fridge i'll use that area.