I think it’s only the V3F25 drives that monitor the main brake. All others don’t even look at it. Check that one is picking good. Make sure the shoes are straight. If it’s kicked, the shoe has separated from the core and the whole thing needs to be replaced. The switch will still pick but the pad can hang up. If they look OK, I would adjust them both with feelers, nice and square. That being said, tach/Encoder is always a good guess for vibrations/shaking.