In survival mode, every time I go out for hunting, my inventory is filled with the unstackable lootbags. I tried to use the stacksize mod to make it stackable, but it made lootbags to work buggy. So I want the lootbags to be stackable and work correctly when stacked.
I use MC1.10.2 but I want you update for all Minecraft versions.

The bags use NBT data for their inventory, which is attached to the ItemStack, as is the number of items in the stack. If I were to make the bags stackable, I would introduce multiple new bugs and dupe glitches (which I've pretty much removed at this point) related to having that data interact and overwrite that I would then spend fixing instead of creating new content. I don't consider this a valuable use of my time for a relatively minor feature.

Make unopened bags stackable and stacked bags unpoenable is a possible way.

I know this is closed, but I have a potential solution. When a stack of unopened loot bags is right clicked, the opened loot bag would be added to a separate item stack. This could work like filling bottles with water, where it would add them to your inventory or drop them on the ground if there's no room.