What I expected to happen was...:
Log off of my realm using Disconnect in Game Menu and it save world changes.

What actually happened was...:
Log off realm using Disconnect in the game menu. Returned to game shortly after about an hour session without a large portion of that session being saved. This has happened once before on 1.16 release but thought it was a fluke. Interestingly as well I had just upgraded a diamond pickaxe to  a Netherite pickaxe and the previous diamond pickaxe has been removed from my enderchest inventory even though I had it at this current save point.

Steps to Reproduce:
1.  Play seemingly normal session.
2.  Disconnect in Game Menu.
3.  Return to a save point significantly different than it should be.