Got a lake here in KY (Cedar Creek Lake) ... just a few years old (< 6yrs old) ... Stocked with Black Crappie. Original creel/size limit was 9" & 15 fish/day/person. This year, the size limit was taken off, and the creel was increased to 30/person/day. They just didn't grow like expected, and never exceeded 8 inches in any great numbers.
Lake is 784 acres ... average depth is 22' & max depth is 60'.
The size & creel limits were changed to allow for the removal of a greater percentage of these fish, in hopes that the survivors would grow to a more suitable size. It remains to be seen, as to whether or not that idea has any merit ... and will improve the Crappie fishing.
Lots of different ideas on "why" it happened, just none of them are conclusive.
... cp