Another mod-related oddity I noticed earlier on in my playthrough occurred when I picked up Ratslayer. neither the Q-35 nor a standard Plasma Rifle will recognize a mod intended for the Plasma Rifle. However, even with mods that should be compatible in my inventory, nothing shows up in the menu, even on the standard versions of weapons, i.e.
When looking at weapons in my inventory, I can access the vanilla mod menu as intended with X, even on unique weapons, as is intended to be added by WMX.