Losing Items after Logging In

Every time I log into my favorite worlds, so far 4 of them, I have logged in and had nothing in my inventory, xp bar, and enderchest. I lost lots of Netherite, Beacons, Elytra, Diamonds, etc. it's very disappointing because I spent over 400 hours total on all 4 of the worlds. I can't play on my worlds until this is fixed because I don't want to lose anything more.