Human Entitys not showing to some players

So I've been having this issue for a while now. I have my own Human Entity Object and it's also registered as Entity.
When I spawn the Human Entity and I rejoin, sometimes I see them and sometimes not.
Now I made a plugin where the Human Entitys get closed every 10 minutes. But now the server randomly crashes sometimes when the plugin tries to remove the human entitys.
Here's the Exeption I am getting:

Code:

16:40:29 Server|CRITICAL > InvalidStateException: "Cannot schedule update on garbage entity LobbySystem\entities\LobbyNPC" (EXCEPTION) in "src/pocketmine/entity/Entity" at line 1750
16:40:29 Server|CRITICAL > #0 src/pocketmine/entity/Entity(2626): pocketmine\entity\Entity->scheduleUpdate()
16:40:29 Server|CRITICAL > #1 plugins/LobbySystem/src/LobbySystem/entities/TeamHalle(85): pocketmine\entity\Entity->flagForDespawn()
16:40:29 Server|CRITICAL > #2 plugins/LobbySystem/src/LobbySystem/entities/TeamHalle(75): LobbySystem\entities\TeamHalle->update()
16:40:29 Server|CRITICAL > #3 src/pocketmine/scheduler/TaskHandler(137): class@anonymous/home/GameServer/Lobby-1/plugins/LobbySystem/src/LobbySystem/entities/TeamHalle.php0x7f6ee445ca98->onRun(integer 12001)
16:40:29 Server|CRITICAL > #4 src/pocketmine/scheduler/TaskScheduler(179): pocketmine\scheduler\TaskHandler->run(integer 12001)
16:40:29 Server|CRITICAL > #5 src/pocketmine/plugin/PluginManager(654): pocketmine\scheduler\TaskScheduler->mainThreadHeartbeat(integer 12001)
16:40:29 Server|CRITICAL > #6 src/pocketmine/Server(2489): pocketmine\plugin\PluginManager->tickSchedulers(integer 12001)
16:40:29 Server|CRITICAL > #7 src/pocketmine/Server(2264): pocketmine\Server->tick()
16:40:29 Server|CRITICAL > #8 src/pocketmine/Server(2107): pocketmine\Server->tickProcessor()
16:40:29 Server|CRITICAL > #9 src/pocketmine/Server(1691): pocketmine\Server->start()
16:40:29 Server|CRITICAL > #10 src/pocketmine/PocketMine(273): pocketmine\Server->__construct(object BaseClassLoader, object pocketmine\utils\MainLogger, string[25] /home/GameServer/Lobby-1/, string[33] /home/GameServer/Lobby-1/plugins/)
16:40:29 Server|CRITICAL > #11 src/pocketmine/PocketMine(304): pocketmine\server()