(1) DC magnetic force is imbalanced, and we found that one pair has a stronger DC force than others. This should
be able to solved simply by replacing them with magnets have comparable strength to others.
I don't know if this would work, but it might be worth a try:
You've achieved single levitation before, with fairly good stability. Can you try taking each magnet + coil and finding the DC coil current required to hold a mass at a given position? If you can hold the same mass at the same place with all the different magnets+coils, then you're exerting the same force against gravity, so your DC forces are balanced.