That's weird, the server is supposed to reset player's alpha(invisibility) if the teleport failed(either he died or moved) or teleport succeeded. The server is also supposed to reset player's invisibility when player is at 'choose skin' mode if he stays invisible(since we have invisibility potion). It's weird how the player stayed invisible after teleport failed and after 'choose skin' mode, there's supposed no way the server could have missed it. That's the reason why i suspect the last bug report was related to player taking invisibility potion from Mystery Box instead of teleport cmd bug. I've also tried to re-produce the bug as in the video multiple time, but failed so far. Btw, did he see the black sphere after he spawn and did he get any announcement/msg about 'process failed' after he died ? Have you ever faced it or only few same players face it ? If you have a video on the player's side, it could also help to find the cause of that bug.
Anyway, i've pushed a possible fix while waiting for more information. I'm not sure if it's going to work considering how the server failed to reset the player's alpha last time. I simply make server reset player's alpha after the player die instead of at 'choose skin' mode.