Things just disappearing

Can someone please help I’m so over when I have issues I can never report them as I’m not that savvy with phones and operating systems ect. I was playing Minecraft at home on wifi and was logged into Minecraft with my Microsoft account I then ended up going out and while sitting at my child’s school waiting for them I got onto Minecraft but noticed when I went onto my world there was an important chest that had just vanished when I went back to the lobby I noticed that I wasn’t logged into my account on Minecraft prob because I wasn’t on wifi ect but when I got home and logged in the chest was still gone. How can I fix this?