Hi

I updated from 1.18 to 1.19 and all my backpacks dissepeard, is there somthing that can be done to get them back?

Probably not. Upgrading modded worlds between major versions is generally unsupported, for reasons such as what you experienced.

I haven't really changed storage format, but I can't vouch for things like forge or anything else not changing how this works. If you can consistently recreate that a pack that consists only of backpacks which gets upgraded to 1.19 will get contents cleared I may take a look but it definitely is a low priority as many mod devs use major updates to change underlying stuff making upgrades between versions impossible so just having backpacks like wouldn't be enough anyway.

closing as I can't guarantee stability between major versions so if this works it's a plus but if it doesn't it just means a need to restart on a new version and that's it