Same issue happening to me.
Game from PC Game Pass.
I am the host.
My friend plays from steam.
Every time I load I am dragged back to the Hedge, the place I was before the patch was released. With the items I had back then in my pockets, and everything I had disappeared. Any new mutations gone.
My friend does load correctly where he last left it. With his items.
Everything that has been left on the chests is there.
I tried erasing every saved game in which I was in the Hedge, and left only the new save games. But I am still taken back to the Hedge in the same conditions every time I load game.
I tried reinstalling the xbox app, I tried reinstalling the game, I tried not letting the game synchronize.
Same results all the time.
If I save and without leaving the game completely I load the game, everything seems to be fine. But after leaving the game, the saved progress goes corrupt or something.
Has anyone found a way around that it's not leaving everything in chests? I am quite far away from the new content and my friend and me have very short time normally to play. So it's barely unplayable in these conditions...