UCC28C42: TI simulated ,Resistor Heated
It's a part of core reset circuitry. It should get hot when no load is present and it should be cool when max. load is present.
It is possible that you swapped the polarity of the output secondary coil? See dots orientation:



EDIT:

MY bad. It' not a reset circuitry, rather a RC snubber to damp the MOSFET ringing. Your values are not appropiate.