Can anyone tell me what is the cause of this lag?

When i am by myself, with NO other players within sight, my in game ping is what it should be for my distance from the game servers.

However, with a few players nearby my ping shoots up a couple thousand.

My Tracert is 100% normal, my manual ping times are also normal in the command box. But in game, it is so bad that red zones are completely unavoidable when other players are near by. I cannot figure out why it does this, but whenever there is NOBODY else around, i can leave a red zone a fraction of a second before it lands and it completely misses me.

Yet, with only 3 other players nearby in a dungeon group, avoiding red zones that specifically land on me is all but impossible, regardless how fast i move. Hell, i can be moving in a straight line when it lands on me, and i STILL get hit by it.

Yet this does NOT happen when i am alone.

I do 25 man raids in WoW, fill the entire screen with players in Aion, Tera and Guild Wars 2 - without the slightest hint of lag. I have really good internet - otherwise 25 man raids would be impossible. Oh and I am a healer in all of those games - yet ive never experience this much lag.