For what it's worth, I have 380 watts of horizontally-mounted panels and normally see something like 16A on a reasonably sunny day, though the record has been over 20A (there's a Bluesky MPPT booster in there, but I saw 21A once before I installed the Bluesky unit).
Maybe there's something seriously wrong with your wiring (like severe corrosion, or severely undersized wiring). You could certainly use an ammeter to test each panel to confirm that each one is performing to spec. Otherwise, I would look at shading and shadowing: a shadow that covers 60% of one cell will cut the output of that panel by 50%.
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