Every now and then when I am playing, somebody or myself will be invisible in the game. I had an issue with my friend one time because every time we finished a round, we could not see each other. One time recently I was invisible even as a runner (zombie). I don't think this is very fair because when your invisible most mobs ignore you. I do not have any mods installed and never did. I don't know how this is possible but please try to fix it.