I have this pretty much 100% of the time when I'm playing a piano piece, especially an older piece that I've somewhat forgotten. It's not so much that I'm re-learning the notes, it feels more like I'm coaxing the requisite movement back out of my hands. It's hard to explain, like... I can't really start a musical phrase halfway through because I don't know what notes I'm actually playing without the sheet music in front of me. But if I start at the beginning, my hands will do the right thing from muscle memory.

I use to have the same trouble with my locker combo in high school. I could spin the lock open, but I couldn't tell you the numbers.

I would occasionally lose the muscle memory too, for about a week at a time.

I hardly know what my password is.

Every time I change my work password, I commit it to memory for about a day, until it's in my muscle memory. Shortly after that, I can bang it out on a keyboard in easily under a second, but I cannot write it on a piece of paper.