The title explains the problem - Umbral Enhancement III does not work on the Cold Denial-Falling Guillotine Umbral Engram, the weapons have only one final perk. It might be just these 2 weapons, but might be just the engram, I'm not sure.
						
					
					
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	All other weapons have 2 perks except Cold Denial and Falling Guillotine. I just tried all other new weapons.
 
										 
					 
		    