My guess was you had it wired wrong and it wasn’t turning off the charger so you overcharged them multiple times. They could all be damaged which will appear as lower capacity. If you have a way to discharge them one at a time and then charge them one at a time and measure the amp hours in and out you could determine if any were damaged. Personally I think battery balances shorten the life of your cells anyway. I don’t know of a simple solution to your problem.