This strange bug happens to me. Not every time. Almost never when i killed someone. But if I encounter dead body sometimes weapons start slooowly howering vertically to the sky. What could cause this and how to fix?

My Skyrim is very heavily modded

I think it's just one of those physics quirks with the game engine. I've had the same thing happen to me, as well as to my followers sometimes.

Well, it could be mod related, but with so many mod's, who knows ???

Have you any mod's related to weapon's ??? (like: Skyrim Weapon Positioning)

I'm pretty sure that's an engine bug. Nothing can be done about it, to the best of my knowledge.

You've killed your enemy with Paralysis from the Bullseye Perk or from any of the other perks. If you one shot an enemy with an arrow and it triggers bullseye, their weapons will float in the air. This is unfixable unless you replace the bullseye perk or not take it (It isn't worth taking if you can one shot enemies, anyway!).

I remade the bullseye perk to do bleed damage instead and have a 25% chance to ignore all armor on an emey. For what enemies I can't one shot, the bleed damage is far more useful to me than some silly paralysis effect.