30 min to warm up? must be missing the thermostat, and that would explain the rest of the problems, since the engine is not getting warm enough soon enough to prevent icing of the LPG regulator.
you will probably need to drain the regulator, and flush the cooling system and confirm coolant flow through the regulator, and consider adding an "LPG thermostat" to the coolant line that returns coolant from the regulator to the engine