1. You could try powering VSA from a supply separate from the motor supply, to see if noise from the motor supply is affecting it.
2. On your schematic I didn't see a 100nF capacitor, should be ceramic preferably surface mount, connected to the 24V supply or VS near the chip. It is shown on the basic application, you have 10u & 1u but lower value caps have higher frequency performance. Proximity to the chip is usually important also.
Just some thoughts.