I notice an odd phoenomenon while playing guitar: I tried for years to learn how to sweep pick and I almost.........get it. Anyway, I back off for six months, start playing again, low and behold I can do it. Weird.
Anyway, a similair story with my chin up progress. I can't break ten reps no matter what. Then I take a week off, and boom, I got it, 12 strict reps.