Be careful not to get the nocks too loose. Fingers shooters get them loose enough that, holding the nocked arrow straight down, a tap on the string will make the nock fall off. For release shooting though, especially thru a biskit, they need to be tight enough that it still takes a little bit of a tug to pull the arrow off the string.

Do you know how old those nocks are? If they're a couple of years old, it could be they've gotten brittle and need replacing anyway.