Used LAN to enable cheats many months ago to /gamemode back into survival to continue my Hardcore world, kept playing the world, accrued many hours in the world no problem, occasionally use spectator to look around my builds, accidentally log out of world in spectator.  Try to reenter world, starts to load but then freezes on "Loading world" and never loads.  Looked to google and others had encountered this on the Minecraft Forum [Minecraft Forum, fixed it by replacing the level.dat data with data from a new world, meaning the player data corrupted.

Not sure if they will help but the level.dat files are included.