UE4 4.11 Crash in FMemory::Memcpy(Engine code)

Hi, I met a CRASH in 4.11, and this happened in engine code.

this is mutiplayer game, it will crash in server. when 4 people play, the game runs well, but if more people play, it will happen.
i attach to the sever use vs2015, and get the crash point, the information is this.

this time the crash seems happend when a playerpawn move and the childactors follow it.

and i debug it many times, not only happend in playerpawn moved.

i wanna to know:

  1. why this happen? is it because the virtual memory is less?
  2. How can i handle it?

any one have idea about this? please give me some clue, thanks a lot~~~