It's because the CONV is converting the protons stacked on top of it into HYGN and the stacked HYGN has nowhere to go, so eventually the CONV becomes BHOL and in most cases the BHOL will be converted by the surrounding CONV into HYGN.  Instead of CONV, try using VOID or PVOD to get rid of the protons.

You never said anything about FIRE.  What's catching FIRE?

If you need the protons to reach the POLO, then set the CONV's tmp2 to protons so that it ignores the protons.  As for the FIRE, I checked and the HYGN didn't catch FIRE; it shouldn't've anyways considering that HYGN doesn't ignite with heat; only FIRE, LAVA, and PLSM.  Check for signs of any of the following elements.

Protons DO turn into PLSM when colliding at high enough speeds.

My guess is that the photons are already at that speed from the moment they're spawned and the protons inherit that speed.  Try using DCEL or VSNS/FILT to slow down the photons before they split the HYGN.