Minecraft Version: 1.12.2
InventoryTweaks-1.63.jar

for some reason my game crashed when trying to sort my inventory with middle mouse click..it's never happened before...but here's the log.

https://pastebin.com/SURWiC4b

Hello, I can confirm this issue. It also happens if you try to shift-click an item into a full container, or an item whose count would overflow the maximum stack size.