While a player's death animation is playing, they can still see updates around then (blocks changing, entities moving, etc.). After the animation is over, no updates are visible anymore. I assume this means that no chunk updates are being sent to the client.
If the chunks around the dead player are not loaded by other means, they invisibly unload after 1 second (after the death animation). This is likely intended, to stop items from despawning when dying while AFK.
Linked issues
Comments 7
After the death animation has finished, the player is no longer loaded in the world
Chunks no longer load around the player and commands cannot target a no longer existing player
Please check if that's still an issue for you in the latest 1.16.4 stable release or the latest 1.17 development snapshot.
If anyone is confused about the edit history: The game confused me, so I reported one thing, then added more symptoms of it, then removed the initial symptoms, because they are likely intended, just unintuitive.