I think that is because you declare 125px for each row:
<detail>
<band height="125" splitType="Stretch">
but use only 20px of that:
<reportElement stretchType="RelativeToBandHeight" x="0" y="0" width="209" height="20"/>
Try to make detail band as height as you use (20px):
<detail>
<band height="20" splitType="Stretch">
I'm not sure, because I didn't use Jasper for a few months, but try this.
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