No I did not switch batteries around, they are not all identical batteries (all are true deep cycle though for antimony) and my wiring is not equal so it is not science. Could be a false interpretation I guess.
PT did warn me here in the past that the middle battery would be undercharged by using this unbalanced method pretending it was a bank of two, so I figured that was the explanation. (I know the right way with buss bars and equal length wires, but can't do it that way)
Perhaps if you have a clamp on ammeter you could spot if one battery is taking fewer amps than the others when the whole bank is being recharged.
After you do some 50-90s camping and go to shore power, then next day when they are nearly full, check their SGs. If one battery's SGs are lower than the other two's, then you know. That's what I get. I don't know if they would even up after several days either. I go right ahead and get them all to 100% individually now that I have shore power.