Die in the nether portal for no reason and my stuffs are gone

While I was playing local I go back to the overworld and then it’s lagging and then I suffocate as if I was in a wall, all my stuffs are gone, this is very frustrating I lost something rare and a whole diamonds armour while it’s not even supposed to happen.

I’ve read this has happened to some people years before and apparently the bug is still here.