Some (but not all) players suffocate in a wall when they teleport. We have a command block on our snapshot server that uses the spreadplayers command, however, after a few hours and several players, it seems new players take suffocation damage whenever they are teleported. We tried teleporting these players manually and the same thing happens. In fact, we forced the players into creative, teleported them and then when we forced them into survival they would immediately die to suffocation damage.

I haven't been able to reproduce the cause but it seems that once a player is affected by it they will always die upon teleport. I am speculating that it is affecting new players that havn't logged into the server before.