I removed 2 ranks from a player and when I try to join back it gave me this error.

[NorixDevelopment]

[15:09:43] [Server thread/CRITICAL]: ErrorException: "Undefined offset: 0" (EXCEPTION) in "plugins/RankSystem.phar/src/IvanCraft623/RankSystem/session/Session" at line 116
[15:09:43] [Server thread/CRITICAL]: #0 plugins/RankSystem.phar/src/IvanCraft623/RankSystem/session/Session(116): pocketmine\utils\Utils::errorExceptionHandler(integer 8, string[19] Undefined offset: 0, string[107] phar://E:/Desktop/DevServer/archive/plugins/RankSystem.phar/src/IvanCraft623/Ran, integer 116, array[0])
[15:09:43] [Server thread/CRITICAL]: #1 plugins/RankSystem.phar/src/IvanCraft623/RankSystem/session/Session(283): IvanCraft623\RankSystem\session\Session->getNameTagFormat()
[15:09:43] [Server thread/CRITICAL]: #2 plugins/RankSystem.phar/src/IvanCraft623/RankSystem/session/Session(217): IvanCraft623\RankSystem\session\Session->updateRanks()
[15:09:43] [Server thread/CRITICAL]: #3 plugins/RankSystem.phar/src/IvanCraft623/RankSystem/command/RanksCommand(187): IvanCraft623\RankSystem\session\Session->removeRank(object IvanCraft623\RankSystem\rank\Rank)
[15:09:43] [Server thread/CRITICAL]: #4 pmsrc/src/pocketmine/command/SimpleCommandMap(248): IvanCraft623\RankSystem\command\RanksCommand->execute(object pocketmine\Player, string[5] ranks, array[3])
[15:09:43] [Server thread/CRITICAL]: #5 pmsrc/src/pocketmine/Server(1809): pocketmine\command\SimpleCommandMap->dispatch(object pocketmine\Player, string[33] ranks remove TitaniumLB5671 Admin)
[15:09:43] [Server thread/CRITICAL]: #6 pmsrc/src/pocketmine/Player(2353): pocketmine\Server->dispatchCommand(object pocketmine\Player, string[33] ranks remove TitaniumLB5671 Admin)
[15:09:43] [Server thread/CRITICAL]: #7 pmsrc/src/pocketmine/network/mcpe/PlayerNetworkSessionAdapter(239): pocketmine\Player->chat(string[34] /ranks remove TitaniumLB5671 Admin)
[15:09:43] [Server thread/CRITICAL]: #8 pmsrc/src/pocketmine/network/mcpe/protocol/CommandRequestPacket(54): pocketmine\network\mcpe\PlayerNetworkSessionAdapter->handleCommandRequest(object pocketmine\network\mcpe\protocol\CommandRequestPacket)
[15:09:43] [Server thread/CRITICAL]: #9 pmsrc/src/pocketmine/network/mcpe/PlayerNetworkSessionAdapter(109): pocketmine\network\mcpe\protocol\CommandRequestPacket->handle(object pocketmine\network\mcpe\PlayerNetworkSessionAdapter)
[15:09:43] [Server thread/CRITICAL]: #10 pmsrc/src/pocketmine/network/mcpe/protocol/BatchPacket(130): pocketmine\network\mcpe\PlayerNetworkSessionAdapter->handleDataPacket(object pocketmine\network\mcpe\protocol\CommandRequestPacket)
[15:09:43] [Server thread/CRITICAL]: #11 pmsrc/src/pocketmine/network/mcpe/PlayerNetworkSessionAdapter(109): pocketmine\network\mcpe\protocol\BatchPacket->handle(object pocketmine\network\mcpe\PlayerNetworkSessionAdapter)
[15:09:43] [Server thread/CRITICAL]: #12 pmsrc/src/pocketmine/Player(3325): pocketmine\network\mcpe\PlayerNetworkSessionAdapter->handleDataPacket(object pocketmine\network\mcpe\protocol\BatchPacket)
[15:09:43] [Server thread/CRITICAL]: #13 pmsrc/src/pocketmine/network/mcpe/RakLibInterface(169): pocketmine\Player->handleDataPacket(object pocketmine\network\mcpe\protocol\BatchPacket)
[15:09:43] [Server thread/CRITICAL]: #14 pmsrc/vendor/pocketmine/raklib/src/server/ServerHandler(95): pocketmine\network\mcpe\RakLibInterface->handleEncapsulated(string[15] 127.0.0.1 59173, object raklib\protocol\EncapsulatedPacket, integer 0)
[15:09:43] [Server thread/CRITICAL]: #15 pmsrc/src/pocketmine/network/mcpe/RakLibInterface(109): raklib\server\ServerHandler->handlePacket()
[15:09:43] [Server thread/CRITICAL]: #16 pmsrc/src/pocketmine/network/mcpe/RakLibInterface(99): pocketmine\network\mcpe\RakLibInterface->process()
[15:09:43] [Server thread/CRITICAL]: #17 pmsrc/vendor/pocketmine/snooze/src/SleeperHandler(113): pocketmine\network\mcpe\RakLibInterface->pocketmine\network\mcpe{closure}()
[15:09:43] [Server thread/CRITICAL]: #18 pmsrc/vendor/pocketmine/snooze/src/SleeperHandler(75): pocketmine\snooze\SleeperHandler->processNotifications()
[15:09:43] [Server thread/CRITICAL]: #19 pmsrc/src/pocketmine/Server(2155): pocketmine\snooze\SleeperHandler->sleepUntil(double 1626793783.8164)
[15:09:43] [Server thread/CRITICAL]: #20 pmsrc/src/pocketmine/Server(1992): pocketmine\Server->tickProcessor()
[15:09:43] [Server thread/CRITICAL]: #21 pmsrc/src/pocketmine/Server(1586): pocketmine\Server->start()
[15:09:43] [Server thread/CRITICAL]: #22 pmsrc/src/pocketmine/PocketMine(291): pocketmine\Server->__construct(object BaseClassLoader, object pocketmine\utils\MainLogger, string[29] E:\Desktop\DevServer\archive, string[37] E:\Desktop\DevServer\archive\plugins)
[15:09:43] [Server thread/CRITICAL]: #23 pmsrc/src/pocketmine/PocketMine(321): pocketmine\server()
[15:09:43] [Server thread/CRITICAL]: #24 pmsrc(11): require(string[84] phar://E:/Desktop/DevServer/archive/PocketMine-MP.phar/src/pocketmine/PocketMine)

[IvanCraft623]

Confirmed bug, in a few minutes it will be fixed.

Thanks for opening the issue.