I got on Minecraft around 10 last night and when I went in my Minecraft survival world it put me back at spawn and my inventory and armor was gone

I got on Minecraft around 10 last night and when I went in my Minecraft survival world it put me back at spawn and my inventory and armor was gone. I looked up how to fix it and found out that you need to save and quit then join it again. It worked but every time I go to play Minecraft this happens and it pisses me off. Minecraft please help solve this issue. I don’t know if the system thinks I’m a different player but please help me out. Thanks