End flashes are not rendering in the provided world when the game is not frozen, although the sky light does change color when they occur. I have experienced crashes while in the end in this world, and while I believe these are caused by MC-312064, I’ll upload the crash logs here in case they are helpful. (I may have submitted one of them previously through the launcher.)
World file is quite large so I’ve uploaded it here. Crash logs are not visible to regular users due to a Mojira bug.
Environment
macOS Tahoe 27.0
This was due to a repeating command block which applied 1 second of darkness to the player, hiding all end flashes only while the game was not frozen (due to MC-269270).