After looking at the world, it seems like each gun has two object sync components, which is in itself a tiny issue, the second issue is that you try to destroy the object instead of using Reap when you let go of it. Which means that the object is never removed and the object sync is still in effect, this makes the map behave gradually worse the more object are spawned and destroyed. "Reap is a function you call on objectsync, and the objectsync needs to be on the top level parent of the prefab."
For reference, in Z0NE's world Ridge Racer, there was 5 object sync component per player car, plus 5 object sync components per AI car for a total of around 150 object sync components. It resulted in awful sync for all non master players, after removing all non necessary object sync the map now has only 30 object sync components and it works almost perfectly for everyone.
All of this is due to limits put in place to avoid bleeding money because of allowing for unlimited syncing of everything. Syncing is now limited, but a lot can still be done within that limit, as long as it's setup in a way that uses the least amount of object sync active at once as possible.
We're still working on making it look better though, but make sure to modify what you can on your content for the tests to be appropriate !