• Minecraft 1.20.1
• Packed Up packedup-1.0.30a-forge-mc1.20.1
• Core lib, 1.1.17a forge

Steps to Reproduce
shift left click crashes game when transfering an stacked item from backpack to player inventory

Crash report (~/logs/latest.log)
latest.log

Caused by: java.lang.IndexOutOfBoundsException: Index 57 out of bounds for length 46
at jdk.internal.util.Preconditions.outOfBounds(Unknown Source) ~[?:?]
at jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Unknown Source) ~[?:?]
at jdk.internal.util.Preconditions.checkIndex(Unknown Source) ~[?:?]
at java.util.Objects.checkIndex(Unknown Source) ~[?:?]
at java.util.ArrayList.get(Unknown Source) ~[?:?]
at net.minecraft.core.NonNullList.get(NonNullList.java:47) ~[client-1.20.1-20230612.114412-srg.jar%23752!/:?]
at net.minecraft.network.protocol.game.ServerboundContainerClickPacket.handler$fgh003$smoothswapping$onInit(ServerboundContainerClickPacket.java:558) ~[client-1.20.1-20230612.114412-srg.jar%23752!/:?]

The error occurs in a mixin from smoothswapping, so I would guess it is caused by that mod. Could you check if the issue goes away if you disable that mod?

sure!

yep, that seems to cause the crash, smoothswapping is incompatible

I don't think there's much I can do about it as the error occurs in a mixin from smoothswapping. I'd suggest reporting the issue to them.