Clearcoat has frosty haze

Like the others, I suspect blooming.  This is the prime season for it.  It is partly a relative humidity function, partly absolute humidity.  Mid-summer is when you have high absolute humidity (dew point). Keep an eye on weather reports, most TV weather guys do report dewpoint in summer.  Lacquer is best at dewpoints in fifties.  Never paint with lacquer when it is raining outside.

Yet again, I would second Phil. Blooming can sometimes occur with clears that have seen better days & often happen with automotive clears that are in aerosol form.

Usually & polish (if you can do this on your subject) with something like light Farecla or 3M perfect-it will remove the problem.

It sounds as if it could be symptomatic of "blooming" caused by high humidity.

Is it a flat or a gloss clearcoat? If you are getting a cloudy finish with a flat spraycan clearcoat, it may be due to insufficient shaking of the can before spraying. When using any sort of spray can, shake for at least five minutes before use and shake occasionally between passes while spraying.