How you mount your flight controller? 30 inch propeller could make crazy vibrations, try mount your controller on vibration-isolation structure, for large drones, this always has to be designed carefully.
Try remove differential parameter(by setting them to zero), keep P-term and I-term in attitude control rate and adjust them patiently, then fly the drone with a remote controller manually in manual/stabilized mode, don’t try position/hold/mission before you are satisfied in manual flight.
Of course, before all that, you should mount all parts of your drone properly, tight and stable.