Windows 10 Java Edition

Happens in both vanilla 1.18.1 client and Optifine client

After some testing I was able to reproduce it on a vanilla server with the following command block structure.
But it is easier / faster to get this in spigot than craftbukkit / vanilla.

The issue happens when you fly behind the the falling sand so that it constantly is on the border of the tracking range and switches between being in / out of it.
When the issue happens you can see in the client log an error, that the falling block is already added to the client. I suspect therefor this is caused by a Spawn Entity packaged arriving before the Destroy Entities package.
That this issue is easier to replicate / notice on spigot can be because spigot modifies the entity tracking range.

@md_5

As I said, when lots of falling block entities with high velocities are spawned some will bug out in the air like that. I also left the name of the plugin used to create this bug but that shouldn't be necessary, just simply spawn a ton of falling block entities like this and you will see (Just make sure when you spawn them in you follow them fast to keep in your render distance)

for (int i=0; i < 10; i++)
    for (int ii=0; ii < 10; ii++)
        world.spawnFallingBlock(p.getLocation().add(10-i,5,10-ii), Material.STONE.createBlockData()).setVelocity(new Vector(2,2,2)); 

Reproduction code....