Not sure if it's when equipped with lament that causes this issue, or on strand, but the Medieval champion mod rarely works properly. I've swapped subclasses around, equipped and unequipped weapons, removed lament, equipped lament, etc. and it is incredibly inconsistent to get activated. Resetting the artifact also does not fix this. I've tried multiple glaives (Judgement & Enigma) and both are affected in this way. EDIT: Just did a nightfall and ran out of lament ammo halfway through. Swapped to wish ender + judgment + linear and unstoppable glaive worked fine. It seems like it's an issue when Lament is equipped for sure.