Originally Posted by Malc
The regulator is not freezing, the propane in the tank freezes and does not evaporate properly. Keep a full tank
Propane in a cylinder "freezes" at -44 degrees, at which point it will not longer produce vapor. So that is not likely to be the issue.
Since it happens with multiple tanks that means the likely source is a regulator OR a constriction in the piping itself. As I mentioned, a local propane dealer may be able to pressure and flow test the system without taking it to an RV dealer. I am still guessing that you have a pinched line or guncked up fitting that is restricting the flow to the furnace.
If you could run a separate line from a cylinder directly to the furnace that would check that out, but a better plan would be to have a propane dealer test the line pressure under flow to see how much propane can flow through the line.
Popping in the middle of operation is NOT a good thing.