There are a LOT of things to unpack here. I only looked back a bit, not the whole shpeel.
I am unsure what BMS those SunGold packs use but they look like Seplos/Pace/TDT without Active Balancing. NONE of those will reset to 100% until 1 cell has hit High Volt Disconnect.. it's a known quirk that MANY BMS' have, even the older JK's, Daly's & JBD's.
The only way to resolve that is to set the High Volt Disconnect lower to something like 3.550 which a runner cell will hit before the rest.
NOTE that some BMS' are Feature/Function locked and some setting changes/adjustments may be disabled.
Part of the issues are DIRECTLY related to the charging profile in use...
Bulk/Absorb: 55.2V for 60 minutes (3.45vpc)
(some call this boost) this rarely actually runs the full 60 mins because of EndAmps
Equalize: OFF
Float 55.0V (3.437vpc)
MIn Volts: 42.4 (2.650vpc)
Max Volts: 57.2 (3.575vpc)
Rebulk Voltage: 51.2 (3.200vpc)
End Amps/Tail Current: (*1)
(*1): End Amps is calculated as follows, 100AH X 0.05 = 5A, 280AH X 0.05 = 14A.
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.
!!! Install a Smart Active Balancer
There are different ways to do so depending on BMS in use... ALSO SunGold may nullify warranty do BEWARE !
Set to start Balance @ 3.200, when cell delta is over 0.010V.
NB: Active MOVES power from Hi to Lo cells and does not waste it. When not running it uses nothing.
It CANNOT fix a bad cell and in some instances where you have a bad cell that won't take charge above a certain voltage, active can end up trying to fill that 1 cell until all other cells in that packs are down to that point. IF that is teh case, the ONLY solution is to replace that defective cell.
BULK & ABSORB (there is confusion because different companies "play" with the terminology.
BULK is CV-CC (plain & simple)
ABSORB is also CV-CC but is usually restricted to a Timer or BMS Control.
FLOAT is Constant Voltage Variable Current as this will allow the current to reduce as IR increases while still able to increase current to service any loads from solar.
~ THE BAD NEWS NO ONE LIKES TO HEAR ~
The "Lowest Common Denominator" rules the battery pack AND the battery bank.
If you have 16 cells and they are matched (IR across working voltage range) they will work essentially in unison, no problem. But if 1 cell is unmatched it will become a "runner" which may either lose or take charge faster or slower.
That means if it hits Hi Volt Disconnect before the others it will "pause" the BMS till that cell settles down, meanwhile no charge is going in...
It also means that during discharge, that cell hits Lo Volt Disconnect, the pack stops discharging, even if the other cells are all higher voltage.
In essence, a Hi Runner will limit the pack because the lowest cell will Rule and all other cells will be lowered to that level.
If you have 5 packs in parallel and 1 pack stays lower than the rest, the rest will backfeed it to balance the entire bank (at pack level).
From my resources, may be helpful to have handy.