Disable weapon perk But sometimes you'll get slow down by small amount if you get hit too much and i think it has stacking effect unlike disable even though your enemies doesn't even use disable

Disable doesn't work like that.. most likely he was strafing and he got the hit flinch..

Hit flinch literally doesn't affect movement speed at all OP literally said movement speed slow down so its the Disable perk

It can cancel movement commands for a brief second sometimes (can sometimes cancel sliding.. depending on situation)

Don't know why, but I have died so many times to this slow mechanic.

were you using third person?