@Inject(method = "onSlotClick", at = @At("HEAD"), cancellable = true)
public void QS$onClick(int slotId, int button, SlotActionType actionType, PlayerEntity player, CallbackInfo ci) {
    if (slotId > 0 && slotId < slots.size()) {
        Slot slot = this.slots.get(slotId);
        if (slot != null && slot.inventory instanceof PlayerInventory)
            if (hasItem()) {
                if (Util.areItemsEqual(slot.getStack(), getOpenedItem())) {
                    ci.cancel();

                    // The code below seems to cause the crash (on 1.17.1)
                    // I tried just removing the whole if block
                    // And it looks like just calling ci.cancel() is enough for the client to get the slot update, at least from the little bit of testing I've done
                    // I had no issues with the shulker box disappearing when clicked on. It acts as if I'm supposed to be unable to click on the slot with the opened shulker box, matching the behavior in 1.17.
                    // Additional testing is probably required though, as there has to be a reason for this block of code to exist
                    if (player instanceof ServerPlayerEntity) {
                        ServerPlayerEntity sPlayer = (ServerPlayerEntity) player;
                        sPlayer.networkHandler.sendPacket(new ScreenHandlerSlotUpdateS2CPacket(syncId, slotId, slot.getStack()));
                    }
                }
            }
    }
}

@Unique
@Override
public void setOpenedItem(ItemStack openedItem) {
    // Commented out the if statement below, the this.openededStack = openedItem statement is intact.
    // Again, there must be a reason for this line of code to exist, but from the limited testing I did, I was unable to reproduce the issue with the ender chest disappearing when clicked on.
    if (!Util.isEnderChest(openedItem))
        this.openededStack = openedItem;
}