crappie lites question?

my wife and i just started crappie fishing last year,we went last week and put a lite off a dock and we never saw a fish come to the lite, but we caught 19 one over 3 pound,this week we went to the same place we had dozens of big crappie come up to the lite, and fished from dark to daylite and caught none,we didnt attract and minnows but there were millions of little bug like creatcures, not sure what they were,the crappie would swim through them swimming eratic,even laying on there sides, looking very strange,what was happening?

they were probably feeding on these bugs - the lights attract plankton and different bugs. If minnows didn't show up the crappie probably did to feed on whatever what was available.