https://youtu.be/kWeFX8JKHZ4

Try to replicate that without other mods and in a LAN world, not on a random server.

Try to replicate that without other mods and in a LAN world, not on a random server.

Try to replicate that without other mods and in a LAN world, not on a random server.

Only EntityCulling

Try to replicate that without other mods and in a LAN world, not on a random server.

This is pure Paper server with only important plugins.

It's still a heavily modified client and server. If players just stayed invisible that would have been noticed long ago with millions of downloads of 1.16.5 forge.

Just looked it up, you are running a hackclient, so a) not vanilla and b) unsupported. I won't add workarounds for badly coded hackclients.

Here's the only way to fix it
"tickCulling": false in config

Pure LAN server