Based on this quote "static friction in bipropellant valves introduce a lag that the control system couldn't handle" It sounds like the fuel valves which contr

Based on this quote "static friction in bipropellant valves introduce a lag that the control system couldn't handle" It sounds like the fuel valves which control the engine's throttle took longer to turn up or down the rocket than expected. The control system that is constantly processing rocket position and turning that into throttle outputs couldn't handle how long it took for decisions to turn into actions. That tends to cause wobbling in most controllers (overshoot, undershoot, etc).