As far as I’m aware the only mods I have that modify speed of weapons at all is Mortal Enemies, and it affects the speed at which NPCs can turn mid swing not the actual speed of the attack? I think? But the end result is followers from Interesting NPCs, or at the very least Anum-La since I haven’t gotten a chance to test any others, are attacking so quickly I don’t even see their weapons move.
It’s quite a list so it’s entirely possible, maybe even extremely likely, that some conflict is happening somewhere. Started a new Skyrim game with a new mod list.