[BrianG]

Hmm. Have you manually checked those cells with a voltmeter to ensure the voltage are close? What you describe sounds like it is specific to that 2s+2s pack. It sounds like the Hyperion is simply shutting off due to high imbalance and the other charger is reducing the charge rate to keep the cells within tolerable voltage limits - simply two different methods to help protect against overcharging the high cell(s).