If you open a chest while falling into a nether portal, the game will freeze chests and inventory. Chests will be bugged into the open state if activated, and will not be accessable. This is fixable in local worlds by save quitting, but realms will resort to a backup after a few seconds rather than restarting the server, causing reversal of progress.

Replicate by sprint jumping towards portal and activate chest while falling in, usually it will just close the menu but after a few attempts this will be replicated. Attached images are from a realm where a backup was resorted to a few seconds after screenshot, and a local test world that was fine after a save quit, but caused inventory and ui freezes. Local world can still be modified after the bug and before the save quit and no progress is lost. Going through the portal is also not necessary, just entering the block to exit chest ui. Screen animations are also off if this is helpful for bug tests.