Welcome to the forum! I haven't had any trouble with mine, but it's very new still and I haven't opened it up too much. However, I can say from experience on my other SUV, colder weather seems to make my rear window easier to close - perhaps due to the pressure in the shocks being less than when they're warm / hot. A little like tires having less pressure when cold. Just a thought. Have you brought this to the attention of a Service dept.?
Sounds like the gas shocks on your tail/liftgate are loosing the gas out of them which lets the pressure bleed off and lets the tailgate close. Sounds like its time for a trip to your service department for a new set of gas shocks.