Unwind
Unwind is made by one person. Write to mago.abdurashidov@gmail.com and a real person will read it, usually within a couple of days.
It helps to include your device, your iOS version, and the level number if the problem happens on a particular puzzle.
Progress is saved on your device only, so deleting the app deletes it. There is no account to restore from. If your progress vanished without the app being deleted, please write in - that is a bug and worth fixing.
Yes. Every level is checked by a solver before it ships. If one seems impossible it is almost always a snake that needs moving in a different order - but if you are certain, send the level number.
They start at level 8 and there is currently no way to remove them. Ads are what pay for the game being free.
Settings → Ad privacy, inside the app.
It is in testing and should follow shortly after the iOS release.