[Konstantinos]

When you disable the spectate, it respawns the player automatically. You'll need to store the player's position while executing /spec command and after they do /specoff, it will re-spawn them. You'll need to add in OnPlayerSpawn to set the position to the last saved one.

It's supposed that you need to do /specoff first and then /spec to spectate another player. It's not that difficult to remove that line and re-spectate the new player!