Some puzzles have more than one solution but the game only accepts one of them. For example the second puzzle has a 1 and 5 in the 1st and 3rd columns which are mutually exclusive with each other in two places.
You could put a 1 and 5 in the 1st and 3rd high up and then a 5 and 1 down low *or* you equally validly could put a 5 and 1 in the 1st and 3rd high up and then a 1 and 5 down low as there's nothing in that puzzle to exclude either possibility and I've checked and checked and checked.
Yet the game only accepts one of those.
Please do not redo the game though. It's frustrating to have to redo all the puzzles because you upload a new version and then all the work done on an older version is cleared out. I'm already having to repeat puzzles because you've changed the game since the first time I played it.