Hi, this is my post here, I 'm trying to catch up with the forum.
Supposing you have made the whole setup by yourself, are you sure that ALL panels are connected using the same polarity? If yes, then I suggest you measure all diodes in the panels' connection boxes. Try to do it night time, disconnect the diodes from box, if necessary.
A second thought: Use a voltmeter to check the voltage on each panel.
A third thought: Use an amp meter on each array.
The (V total x Amp total) should give you the absolute wattage.