Added/Fixed Stop the glitch please?

So over the recent few months I've clicked tab to see who is on and when I see someone's name in chat and it isn't In the tab I think they're vanished but to those who are in front of me chatting but not in tab I think its something to do with a glitch for the tab its also pretty annoying when I try to ./tp to them it says Player is offline or something like that
I want to know if this is a glitch or what?

Also the disguise glitch is it fixed or not because I can't disguise as other players it says (You have been disguised) but I asked different player if I am disguised they say "No" so is it a glitch or am I doing it wrong?