Times when a planet(not Earth) is not 'round'-
Mission of Gravity - Classic science fiction novel about an alien planet that is lozenge shaped because of very intense gravity.
Goblin Slayer - Manga is a 'four cornered table' in which the gods play Dungeons and Dragons type games.(Please note this series is very much NSFW cause of extreme violence in general and extreme violence against female characters.)
Golden Sun - Video games and the world is flat. . .may be some super science and/or magic involved that turned a round world flat but series never made it past the third game so no one will ever know the truth.
Discworld - Fantasy books which planet is flat cause magic.
Also if our Earth is flat then cats would've pushed everything over the edge by now.