This movie generates the save files required to play back the New Game+ Neutral movie file correctly.
UNCHECK Runtime > Prevent writing to disk before playing this file back to ensure it generates the files correctly. Also make sure Movie >Auto-restart game is on. Oh and make sure Runtime > Time tracking > clock_gettime() is checked, otherwise the game won't progress past the intro/first couple frames.
Save files can be found at /home/YOUR_USERNAME/.config/UNDERTALE_linux_steamver. Make sure to delete existing save files before playing this movie.