Mantle, Earth Problem?

[Silverdex]

Hi there. Just wanna ask if there's a problem in that map. I played there for several solo games and 2 of my games failed(I had to abort the Mission), because in the field where the toxin injection was located, a single mob disappeared from my site. After he jumped down to the ground from a tower(located at the middle of that field), he goes THROUGH the ground like there's a hole in there. And the next few moments I tried to locate him with my codex while he tries to shoot me continuously, and I can't find him. So, there it goes, aborting my game. Is this a common problem to the game? Thanks in advance(for leaving a reply)! :)