Hi, this issue just recently surfaced when I was playtesting my game.
For some reason, the arms in the animation appear to just stay in (relatively) the same position. I don’t remember modifying or publishing new sets of animations onto these, as other weapon animations have been affected.
Help!
Yeah sorry I have to bump this. It’s still plaguing my game, please help!
I think alot of folks are having animation issues lately. I’m pretty sure it has to do with the recent animation updates to the engine. There was an animation throttling update and another update to animation blending as well as another that provided higher priorities. Updates to Animation Throttling - #44 by Jaco2811
Oh! I thought it was some kind of animation error on my end 
Thank you!
I might be late but I’m having the same issue, have you found the solution Sensei?
The slash animation has same priority as the idle animation and will blend (even if weight = 1)
Either stop idle while slashing or make the slash animation a higher priority, like Action2.
I think it was because of animation priority issues. Try setting the idle to the lowest possible animation priority (in this case, Action since Idle / Movement are taken by the default roblox character animations), then have everything else at least 1 priority higher. Action2, Action3, etc…