When I Play Minecraft pvp on any server, there are invisible Players, who kill me, because I can't see them.
The first time, when I notice that, was on this server: SCB5.minecraft.to (SCB1. - SCB20.)
Every time when I start a new Game, I can't see anyone. But after a Player died, I can see him.
It was only on this server for a few weeks, but now it is on very popular servers like eu.hivemc.com.

On servers with respawn iT's not a big Problem, because I can see someone after he respawns. But on servers like Trouble in Mineville it's a very big problem.

Sorry for my bad English... I'am German