You are at too low a voltage n the main charging leads or the charger is detecting a cell that is below 3.2V. Try checking with a voltmeter at the connectors that plug into the charger. If the main leads are below 19.2V or any cell is below 3.2V it is telling you there is a problem with the battery.
With a 6S battery, I am assuming you fly an H920 or H920+.
High C rating but the only impact it has in this case is with the battery price. Minimum C rating needs to be around 20C. Anything over that harms nothing.
As a PSA, that connection break message will also occur if the balance tap plug is separated at either end.