Interestingly, I observed the same when I was practicing the drums. I would fail multiple times to reproduce a drumming part, sleep on it, and succeed on the first try the day after.
Difficult parts on videogames as well. It could be attributed to slow response times due to being tired or accidentally memorizing a bad pattern, resting also could help with those.
This would happen to me when I played pool. I would master a skill overnight, somehow, and come back to the table the next day leveled up--far better than I had left off the day before.
yep, same with guitar. go to sleep fumbling through a riff even though you "know" it, wake up playing it smooth as hell