Broken Bias Button challenge requires to never press bias button.
This challenge doesn't look too hard at first but it is actually pretty hard one to try and get a win on.
Biases add your multi_count multiplied by your bias_count to your powergain.

This bonus doesn't look too powerful at the lower part of the ladder, but the higher you go in ranks, the more powerful it becomes. But the bonus to powergain is not the loss we care about the most in this challenge.
Multi heavily depends of your current ladder_position. The key use for biases is the possibility to instantly change your ladder_position by dropping your point_count to 0, while maintaining your power level.
Combining the dependency of multi of your ladder_position with the disability to change you ladder_position at crucial moments makes you extremely reliant on other rankers and their upgrade levels: blindly following the main group with multi might leave you stuck at the high ranks with little to none powergain. And on the other side, if you stall on acquiring your multi while others power-up normally leaves you far behind.
This makes the challenge as slow as Broken Multi Button, if not slower.
Winning the round is still possible, although highly depends on overall activity in AH-ladder.