I play it on my friend's Xbox save when he was updated, I update his to the new version when we came in, we lost everything we had in our inventory

the same happened to me sorta. my hotbar items and armour got pushed back like 2 real life days but everything in the world is the same like some items in my inventory are the same some aren't all my chest are the same all my buildings haven't changed. it seems like multiple saves have merged or something

Hello LordMaster and Nacki

I'm sorry to hear that you've both experienced this inventory bug! There was a nasty bug that was very similar, and we thought it was completely fixed. However, based on what you're both reporting hear it seems like it has resurfaced. Can you please both submit a support request so we can work with you to get the necessary information to the team to help fix this bug? 

https://support.obsidian.net/contact and include the following information: 

1. Platform (Xbox Console, PC Game Pass, PC Steam). 
2. Multiplayer or Single Player Game (if multiplayer, can you let us know how many players in total in the game and their platforms if you know this) 
3. Description of issue. 
4. Last thing you did in the game before the issue occurred, if applicable.

Thanks and have a great day!