When randomly joining your friend server again your items in your inventory are gone.

So me and my friends were playing on beta Minecrafts and we decided to make a world where we would help and build together and yesterday we're at day 138 in Minecraft and we already has so much progress and the next day which is now I can't join in my friends server because my Minecraft was outdated so I updated it to 1.21.120.20 which is the latest one and after I updated my Minecraft and I joined my friends server my inventory is annoyingly empty. I had so much precious items in my inventory. My other friend also experienced it too. The owner of the world didn't experience it.