Real fun mechanics and difficulty scaling.
@scout2901: I don't know if it's a bug on your side or a nightly update, but today (13/06/2018) there is a "thank you for playing" message, and a "bonus" level showing developer's love for us.
You have to grind hard to advance, and the game is full of bugs (no "money" awarded at the end of the stage, lost upgrades). The real name of the game should be "Grind super buggy 2"