Describe the bug
When trying to either drop items in or shift-click them in, they appear in the bag, but once the UI is closed, and sometimes a few seconds after and interacting with something like a crafting table or other interactable item, the items I just put in re-appear in my inventory, or pop out around me and i pick them back up.

Screenshots
not screenshotable as it happens randomly and quickly.

If it is a crash, please provide the crash-log through a website like http://pastebin.com or https://gist.github.com/
No crash, but happens to me & my partner on a LAN hosted instance of the modpack.

Please provide the version of forge used, and the mod version.
Forge: 36.2.22 (1.16.5)
Mod Version: 2.6.11.2

does it happen to both of you, or just you? are you the one hosting the lan game, or joining it.

Ive never seen version "2.6.11.2" before, but i feel like this is just a fluke or some kind of race condition, no ones ever reported anything like this before, and i cant reproduce it, if you find a way to make it repeatable let me know.

sorry was looking at simply jetpacks.
Simple backpacks version is: 1.16.5-2.0.1-build.27

Happens to both of us, I am the host, with her joining.

Fixed in 2.0.2 in 1.16 / 1.18

could you attach your simplybackpacks_backpack_data.dat file? its under the world save, in the data folder.

edit: also if you could, the latest.log file from a recent play session, i think i know what it is, but i want to confirm.

do you only open the backpack via hotkey?, what tier are the backpacks?

simplybackpacks_backpack_data.zip
latest.log

Hope these help

at the moment the upgrade and migration code is only in the open by hand code, the hotkey doesnt do those checks yet, didnt anticipate the hot key being used exclusively :P
Related to #43

yes they are on the "back" bauble slot, and opened via hotkey.
bth backpacks are currently "diamond" tier

try pulling it out and opening it via right clicking it in your hand, should fix it., in the datafile it was still a common tier, so only the first 18 slots were usable.

o.O that immediatly fixed them.

We had nt opened them by "hand" after upgrading them, didnt realise we nneeded too, or is that just a failure of the back to recognise the upgrade?

I am a bit of a hotkey fan, many of my hotkeys in miinecarft are bound to my stream deck so i dont forget them.

Always love using a hotkey mid game than having the shuffle things in my inventory by hand.