Sometimes when going into the nether (not all of the time, but it happens a lot) my friends and I will get hit by something that we can't see, not even in spectator mode. The death messages vary as well, it has said slain by spider and slain by creeper (note that it said slain by creeper, not blown up) and shot by skeleton, even though in all of the deaths, when the player is getting hit, arrows are stuck in them as if they were shot, even when it says slain by spider or creeper.
Video for reference: https://www.youtube.com/watch?v=ewoF0fgplkE&feature=youtu.be