Myself and other devs in my team are loving the mod so far, however, we've run into an issue upon world loads and then crafting new backpacks. We have learned there might be a problem with your load method. It seems to restart at 1 every time. We think the best way to get around this is rather than scanning the nbt file is just counting up with inventoryIndex. If we find something else that contradicts it, we'll comment on this issue

index = Integer.parseInt(name.substring("inventory".length(),name.length() - ".nbt".length()));

we think this line (72 from BackpackStorageManager.java) is never getting reached when you're searching the files

Jup I now fixed it, I forget an exclamation mark before name.endswith(".nbt")
Thanks for the heads up