Frozen propane regulator

You have a leak somewhere.

Liquid propane entering the regulator could cause that problem. Was the tank recently filled? If so it may have been overfilled. Was the tank upright?

The propane did not freeze. Although as you burn propane the propane evaporates to create gas and further expands in the regulator. Expanding gas reduces the temperature. In your case the temperature dropped the equipment below the freezing point of water and the frost forms. Same effect with a cold margarita on a humid day.

I agree there is a good chance you have a leak and used a lot of propane and created the very low temperature and frost. Propane remained a gas and escaped.

Leak.

If it's a leak the reason the grill went out is the propane tank is empty. Is it empty?? If its not you have another issue. 1/2 inch think frost seems pretty extreme for propane usage in a few minutes as described by OP. The regulator can only allow a limited amount of propane through. In a few minutes to build up 1/2 an inch of frost does not seem to be within normal operating parameters.

High humidity and low outside temps, I have had a 1/4" frost form on active tank when between 1/3 and 1/4 full, makes easy to read level!!!!

It was the first use after putting a new cylinder on the grill. It is possible that I may have not tightened the regulator onto the cylinder quite tight enough, and had a very small leak around the collar and onto the outside of the regulator.

From the time I put it on until I checked on it later was an hour. (I cook chickens 2 hours on indirect heat, and was checking halfway through.)

I will check in the morning and see if the tank is empty. I have already removed and reattached the regulator to the cylinder.