What does "acting up" mean? That's as descriptive as saying "I'm in pain". What does "any condition" mean? Driving in rain, snow, cold, hot? Turning, slowing down, pressing the brake pedal? When not pressing the brake pedal? "Any condition" could include pulling a trailer, a heavy load in back, low tire pressure, or driving on a bumpy road, ... All of which can make anti-lock brakes do unusual things.