Why is my fireball bugging out using tween service?

So, I've used tween service to move my fireball, it is completely fine in Studio but, playing on a Roblox server seems to cause the ball to bug out ( going up and down repeatedly ). I've used body Velocity in the past several times and every time once the is going forwards it tends to stop for a time, then keeps going. SO I stopped using it cause it wasn't smooth. I assumed that the tween was trying to apply gravity or something and even if it is, I don't know how to fix that.

Also, the fireball is unanchored so that it can collide with surroundings.

If there isn't a solution , is there anything better to use for abilities OTHER than tweening.

https://streamable.com/6klwsf

The fireball bugs as it is unanchored as you mentioned where physics is trying to fight with the tween itself. The most ideal method for making a projectile move is using a BodyVelocity and setting the network ownership to nil using SetNetworkOwner. Roblox uses network ownership to either stimulate an unanchored object on the server or the client and using SetNetworkOwner prevents Roblox from doing that automatic behavior. You can read more about it in the following link https://developer.roblox.com/en-us/articles/Network-Ownership

Fireball.BodyVelocity.Velocity = ??? --> This question mark is up to the speed of your projectile trajectory!
Fireball:SetNetworkOwner(nil) --> This sets the fireball's network ownership to the server, which stops the delay behavior.