I've been playing on a multiplayer world (not Realms) with my husband and our friend since the Nether update and when joining the world a couple of weeks ago my inventory, levels, entire Ender Chest inventory etc was completely empty and I was back at spawn. I didn't die before leaving the game or when rejoining, and my usual spawn point is in my house (which is spawn-proof). I ended up losing a lot of items (Netherite armour, tools plus backups in Ender Chest and Shulkers full of items), so we decided to just recreate everything lost in creative and, going forward, I made sure I put everything in my inventory and Ender Chest in barrels before logging off.

Since then, every time I join the world my bed and the one next to it are always invisible (I have to break and replace them to make them show up) but no more items were lost, so we carried on playing. This weekend when joining the game (via lan not invite), all of my Netherite armour, tools and items which I had put in the barrel next to my bed before logging off were missing but the barrel still had some items that I didn't take out that day (spare Ender Chests, shears, sticks). The barrel next to the other bed (which I don't use as my spawn point) was still full of items (including some Netherite tools) with nothing missing.  

My husband created the world in 1.15 and has been playing with his friend since then and I joined after the 1.16 update but neither of them are experiencing similar issues. I'm the only one signed in with a Microsoft account but I can't see that being the problem.

We've now had to make back-up boxes of my items and leave them at different bases just in case this happens again but it's starting to become really demotivating to constantly lose items/inventory on top of lag and other bugs.