If I recall my struggle correctly, it had to do with catching all the changes between the example configurations (older) and the deprecated commands in the newest hy_vfd driver, as well as getting the right motion connection to the driver. This is the last change I made before mine finally worked:
net spindle-speed-cmd motion.spindle-speed-out-abs => spindle-vfd.speed-command
net spindle-vel-cmd-rpm-abs => spindle-vfd.spindle-speed-fb
