I can’t say much here, as I don’t know the exact animations nor has this happened to me before when working with them, but, as it stands, this is most likely a problem with your animations.
If you’re using multiple animations then it’s always a nice check to make sure that you’re not dual-booting the same animations and that they’re not still playing when you try to play another animation, as this takes up memory and can cause problems, possibly including the one you’re encountering.
Another possibility, is that you’re loading an animation that’s higher on the priority list than the others but it’s an empty animations (this, however, HAS happened to me, and is a bit frustrating until you figure it out.)
Sadly, there’s no way for me to directly help you with this, but if you find anything, it’d be nice to hear from you.
Sorry that I’m of little help here, and thanks for reading my reply.
(And I might add, I’ve used referencing tags (objectvalues) with an AnimationTrack value to prevent having to dualboot animations on a single humanoid.)
It turns out I was using BindToRenderStep and a couple of animations were being played/stopped every frame. I made it check for animationTrack.isPlaying and it now seems to be replicating to the server, thanks.