You didn't say what paint and gloss coat you are using, but to attempt an answer to your second question:
Yes, termperature and especially humidity can affect how a coating cures, and one of the effects is on the gloss.
As to your second question, there are a number of ways this can happen. In conditions of cool temperatures and/or high humidity, the reducing solvent can be trapped within the paint on the surface because it did not evaporate on the way to the surface. This could occur in an overly air conditioned room, or a very cool, damp basement. A similar thing can happen in very warm, or very warm and humid conditions—solvent is trapped because the paint "skins over" before the solvent can come out. Aerosol cans are particularly vulnerable to either condition.
In either case, the escaping solvent leaves microscopic blisters or bubbles in the coating surface, resulting in the "frosted" appearance.
There are several potential cures. The easiest is to apply multiple, light coats, allowing each to cure before applying the next. Another thing to do is increase your spraying pressure and/or increase distance between airbrush and model. Yet another approach is to use a reducing solvent that evaporates more rapidly, or such a cosolvent with your reducer.
For aerosol cans, light coats, increasing the distance, and keeping the can warm will help.