Arguments between the MPPT, the BMS and the Inverter have ensued.
One cell, in particular runs, and when the MPPT hits it's shut off voltage, the voltage of the inverter fluctuates wildly, causing issues on the AC side.
Turning the high voltage cut off on the mppt down (28.4-27.2) helps the second issue, but the first issue I'm not sure if I need active balancing, and then whether I need 1 or 5 amps of it.