I know it's been mentioned elsewhere, but only in the medium and hard categories. In this case, I installed the app, opened it up and tried out an easy puzzle. On that very first easy puzzle, I ended up with (afaik) multiple solutions:
1/3 and 3/1 can go in either order here.
While it appears there's some debate over whether or not that's legitimate in a sudoku, it certainly makes it less fun.