Battery #24 looks weak at 12.58 volts...
There is one way to help that battery... Get some 12 volt brake lamp bulbs and wire on some alligator clips. In this case connect the bulbs to the other 3x batteries that are "higher" voltage... And this will give you ~1-2 amps of bypass current to charge the weak battery (if it is "salvageable").
You will have to monitor the voltages across the other cells to make sure you don't take battery 24 over the state of charge of the other batteries.
The series clamp meter current readings are either a bit strange, or simply the level of accuracy with the equipment you have (are you zeroing the DC Clamp meter every so often? DC clamp meters have zero drift over time and temperature).
There do not appear to be any "cross connected" (or ladder connects) between strings? They are all wired in series and paralleled at the 24 volt +/- bus bars?
There should only be "one" current measurement per string (each battery in a single strings "sees" the exact same current).
One other thing to check... You want the battery cables in each string to match overall length. If one string has an "extra long" cable run, it will have more resistance for those batteries and cause them to supply/accept less current. You want to measure the "quality" of the cables and their connections under heavy current (either supplying loads, or charging a discharged battery bank). That is when any cable/resistance issues will generally show up.
Many folks will terminate absorb charging when the charging current falls below ~2% to 1% rate of charge (i.e., a 200 AH battery string, terminate a normal charging cycle at ~4 to 2 amperes). AGMs should have low "leakage current" and will draw well under 1% rate of charge when full. If your batteries ever show a charging cycle tail of >1-2% rate of charge (the batteries never fall below 1% rate of charge with normal absorb set point voltage), the batteries are getting old and need replacing soon. Any batteries that "tail" at >2% rate of charge, should be replaced right away (or taken out of service). They will run hot and can overheat if >2% is pumped through them for hours on end).
There is an "absorb" that some folks (and battery mfgs) recommend for their AGM batteries. Whatever the absorb charging set point is (say 14.4 volts per 12 volt battery or 57.6 VDC on the 48 volt bus bars), hold that voltage for ~8 hours every 6 months. That is the typical "Equalization Charge" for an AGM battery bank.
Your post #7 vs post #14 voltages kind of have me wondering what is going on... post #14 looks pretty good with just battery #24 looking like it can use some help...
Post #7 the batteries look all over the map.
What is the absorb voltage set point (or was this floating)--What was the 48 bus charging voltage from the genset?
I think the main difference between fx and fxr is the grid interactivity. Also, fxr needs mate3 (my fx use the simpler mate). Don't know if the grid stuff would interfere with stacking in an off-grid application. It might, so I'd check with OB. Likewise, check with them on the split bank thing. In theory, I think it may work, but don't know what happens if (eg) a slave bank hits LBCO.