I did accidentally pull down too hard on my screen when I was trying to scroll up, which accidentally refreshed and deleted all my answers on all difficulties, not even just the one I was working on/hadn't solved yet, so that's less than ideal. I almost had level 4 done, but no way I wanted to go back and redo it all!
I'd also love an "answer lock" button, and/or floating undo/redo buttons, because sometimes to take the next step, I need to put in an answer and game out how the rest of the puzzle comes together with that answer, and it would help to be able to undo back to that point, not just try to count my steps and keep scrolling down to the undo button for more of them. I'm not likely to get out a piece of paper or pop open a notepad app to game it out that way.