Custom projectiles are desynced client-sidedly

Custom projectile entities are desynced in the client-side.

When you spawn one, they seem to just float even though the server-side entity is moving or at least have changed positions.

 

I can't show this without a video but here is how to reproduce:

1. Make an addon that adds a custom projectile
2. Get it to move by using a mob to shoot it, or slime blocks.

Expectation:

The projectile should move in the client and server

Observation:

The projectile will only move server-sidedly but the projectile will stay at where it were in the client-side, just floating there.

 

For the addon that I sent, spawn a wither skeleton and replace their hand item with a bow. Then get them to attack you because they shoot a custom projectile