The bug makes players "die" instantly if they receive fall or suffocation damage. it brings up the menu telling the player to quit to the menu or respawn, but in the background, you can still see the health and food bars and the Hotbar. hitting respawn makes the menu go away and the player is still in the spot they took damage and they still have all their exp and items.
also, this causes the player to be unable to get achievements until they reload the game.
I do not have a crash report and I do not have the f3 menu screenshot, sorry for that inconvenience.
I also do not have Optifine or any mods installed, all I know is it occurs between 1.12.2 to 1.16.5.
reloading the world fixes the not getting achievements issue and all achievements that should have been earned during the last session are all given at once.

again I am deeply sorry if this is not enough info