No answer on the temperature question ?
Warms up, pressure increases faster then leaks. Cools down, pressure decreases AND it leaks.
Other choice, put 25 psi in the keg, shut off the tank, shut off the hose. If the pressure on the gauge goes down, the problem is on the tank/reg end. If the pressure holds, after a few hours or over night, open the hose only, see what happens with the gauge. Goes down, keg side problem. Or, it could still be both.