It seems that the client sends an invalid active slot ID after he places a block (HoldingChange, 0x10 packet). The numbers looks random but they are definetely are out of range of the available slot IDs (like 2578) and it cause the server to crash when you perform any action.
Probably it's a temporary client bug, but it could be fixed using the safety check in the ReadHoldingChange() method (PacketHandlers.cs) or even in the OnActiveChanged() method (Inventory.cs).
It seems that the client sends an invalid active slot ID after he places a block (HoldingChange, 0x10 packet). The numbers looks random but they are definetely are out of range of the available slot IDs (like 2578) and it cause the server to crash when you perform any action. Probably it's a temporary client bug, but it could be fixed using the safety check in the ReadHoldingChange() method (PacketHandlers.cs) or even in the OnActiveChanged() method (Inventory.cs).