Sometimes when I kill NPC's their body will ragdoll and fall to the ground like normal but their arm will hang on an invisible point like this.

Spoiler:

Does anyone know what could be causing this?

Thanks everyone!

same here sometimes but i cant figure out what is the problem

Give this a go.

https://forums.nexusmods.com/index.php?/topic/8000718-fallout-new-vegas-bug-hanging-or-floating-corpses/