About the HTM.java-exmaples, the PreviousPredictiveCells is 0 sometimes at run time abonomally, why?

In the HTM.java-exmaples, I am running the exmple NetworkAPIDemo with 100 rows of new data in csv like this:
I print the output of the demo like this:

      sb.append(SDR.cellsAsColumnIndices(infer.getPreviousPredictiveCells(), 32)));

In the output of the demo, I found that, the method getPreviousPredictiveCells will retrun zero cells,which leads the anomallly score =1 , is it a bug? or anything to explain it?

Here is the output: we can see, the prediction is correct , the anomally score should be 0, but it is 1.