The Cotton Alley feels more like a world of concepts that never made it into the first six chapters. To me, it was the most fun chapter, but far from the hardest.

The Cotton Alley light world was way too easy. I finished most of the levels in one sitting.

Try checking the integrity of the game files. If that doesn't work delete all the SMB files (back it up first) and try playing there. If that goes well, just put your save file back in.

I'd like to help test, but I probably won't be able to finish any of the levels.

10420. I thought that was a lot.

The levels felt way too hard for me, especially some of the jumps. The levels look nice though.