Is it a bug or a new feature?
It’s a feature. We decided to create a new puzzle section instead: https://www.codingame.com/games/community
The reason is that this mode was not used a lot and we think that the majority of the users of the 20mn clashes are just looking for more puzzles. We believe that this will profit to more people this way.
20min clashes were often more interesting and more challenging IMO. It would be nice to have a harder challenges sections.