Sometimes when the banner ads at the bottom of the puzzle change, the whole game slows to a crawl. No selectable difficulty. The majority of available puzzles are too easy and solved in 30 seconds or so.
Developer reply
Hello, thanks for your feedback! Please open the app's Settings, choose "Game Mode" and enable "Choose Difficulty" option. Then you'll be able to choose the difficulty level. Kindly contact us via the "Help" section so we can look further into the issue with the banner ads slowing down the game. Thank you!