Giving a generalized reply here.
The first thing to check is the level of coolant in the radiator.
Coolant level falls too low and there may not be sufficient volume of coolant flow through the regulator.
Even though you may have coolant "present" in the regulator, it is imperative that there be sufficient flow of coolant through the regulator to heat it up enough to stay ahead of the cooling effect of the evaporating liquid propane.
I would first make certain that neither of the coolant hoses serving the regulator are kinked nor swollen (swelling may indicate a deteriorated inner lining of the hose resulting in a "flapper type" restriction caused by the hose itself).
Icing that occurs after about 20 minutes is often the result of poor coolant flow rather than overfueling by a defective regulator. You want to test the temperature of both coolant hoses serving the regulator. If you have good coolant flow......both hoses should be as warm as the top radiator hose after 20 minutes of operation. If one hose is cold and the other hose only slightly warm when the regulator begins to ice up, you have a coolant flow issue.
If you can eliminate poor coolant flow then the regulator is certainly processing too much liquid propane.