Panels are nearly perfectly matched, so this is not a panel mismatch problem.
The more info you give us on your system, the less mis-guessing on my part.
What is the SCC Settings for float, absorb, and equalize? 12 volts charging is really low. It should Absorb at 14+ VDC, and float above 13. At 12 volts, not surprising only 2.5 amps go into the battery. These settings should closely match what is on your battery spec sheet.
If you have a way of measuring short circuit amps of one string at a time in full sunshine, you should get pretty close to 5 amps. If you can measure two strings at a time, just watch the amp meter. Most meters I’ve seen that use leads have a fuse that blows at 10 amps, and your two rows of panels will exceed that. A clamp meter may work better.
I troubleshot my 3S2P set up yesterday. Had a dead string. I had two problems. First was the combiner box had a screw that came loose so killed the connection. The second was a pin was pushed in on one of my connectors. This caused a whole series of three panels to not provide power. After I fixed both those problems, the system worked good.