I've had the same 2 hour cycle for about 4 months now and i just noticed his mouth open.
no mucus and yes the cage dries before its time for the next spraying.
My best guess is there's too much moisture in his cage. Try reducing your misting by x2 per day for a couple of days. Dry him out a bit and see if that helps. We recently had the same problem.
ok sure ill give that a try...but what i don't understand is that i had the same misting schedule for 4 months and today was the first time i see his mouth open....weird.. anyway thanks for the help...ill post updates when i have them..