I've noticed this with drums too. Trying out more complex things that required more coordination than I'd typically been able to use up to that point... I noticed that after taking a long break - like 6mo, between bands, etc - with me playing very little in between, I could then sit down and play the thing I couldn't before effortlessly.
Just noticing this exact phenomenon as a beginner learning wing foil: over two days, one day I can barely stand up, and only on one side, feeling very wobbly.
The very next day, I am easily standing up on both sides, and can pump (which involved jumping on the board and jerk-pulling the wing).
There was definitely something happened with my brain while I didn’t train.
One of my friends is a doctornspecialist in treating musicians. He told le once it is a well known phenomenon, and worst, if you practice too much without rest, you can damage your brain in a way that makes it difficult to progress later.
This has been discussed in competitive videogames too. Usually people think that playing more and more is better, when actually having some days without playing is the best way to improve yourself.
Yes, I noticed that doing finger agility exercises (on the piano) implies huge improvements for the day after, while very limited benefits for the same day.
I get a bit better at them immediately, but that plateaus. (Often, I actually start to get worse at it, as I fatigue.)
On returning after a break I'm usually much better at it than my previous best.