I have been experimenting with solar by buying a 10-pack of Hyperion 400-watt bi-facial panels by using two four-panels strings. That has been working great and I am ready to step up my setup to the next level.
I have ordered the following:
EG4 18kPV Hybrid Inverter
2 EG4 PowerPro WallMount...
I am an amateur at this and the following probably has nothing to do with your issue but...
From your picture, the one on the left does not have enough "breathing" room to the left and above it? If that one is not discharging as fast as the right, maybe the temp is a bit warm inside that one...
To follow on to my comments.. the fridge to the left of the one on the left would actually generate additional heat behind the fridge, which might further "warm" the one on the left? Probably not related, but worth looking a temperature graphs of the batteries to compare?