Thanks for such a detailed and helpful review!
Originally, I planned a few more features and mechanics to the game, but with my procrastination and amounts of bugs, I never got it completed. So I ended up with just a puzzle prototype.
Also it was a well needed idea to add the undo and viewing the board on the number assign screen. Another small detail that shows how important playtesting is haha(I got people to playtest it the day after and everyone was talking about the same problem.
Thanks again!