I was sitting at spawn to charge my power armor in the middle of it and went AFK for a bit, but when I logged in, I was 500 from spawn and had lost a Full power armor suit and a Brown crystal pendant.
Presumably you got kicked after being afk for 10 minutes and then had a load issue when logging back in that caused you to "fall through the world" and die? If as you say you were stood in monster spawn/lobby I can't think of any other way you could have died unless perhaps your power armor overheated while charging via solar upgrades (which can happen if there is enough lag as the heat is applied all at once when the server catches up instead of gradually as it is supposed to).
That's what I meant by this, if lag is bad enough then instead of your helmet building up 1% heat every few seconds as it charges from the solar upgrade, which your cooling system can normally mitigate, it can instead jump straight to 100%+ heat capacity and set you on fire for a few seconds while your cooling system tries to bring it back down again... I had it once when my heat jumped from 0 to 4000% in an instant, though fortunately I was in creative mode at the time so it didn't kill me!
Well the thing was is that the death point was 500 blocks away from the center of spawn, so unless the heat channeled into a funnel and I went in a balastic path, then there's no way that I could of moved
