At random times, if you are trying to tp to players while in GM3 using the spectator tp system, it will not recognize them and makes it so you cannot tp to them, even though the player is currently online. The mods working on my vanilla server complain from time to time about it, and it seems that it's been in the game possibly since 1.8, but cannot be certain. Here's a video showing the glitch, however I disabled the sound because of background noise. https://www.youtube.com/watch?v=FdN9DfKWm1U

New video showing problem better here: https://www.youtube.com/watch?v=zgNTuw6ZwiE