Course Hold on chart plotter only works sometimes.

[bmcminn]

I have a Garmin GPSMAP 943xsv chartplotter connected to a Yamaha Helm Master EX autopilot system via NMEA 2000. I'm having an intermittent issue where Course Hold won't engage — it just blinks blue and does nothing. Heading Hold and Track Point both work fine. It's not a speed issue and there's no active navigation/track running. Sometimes fiddling with buttons clears it and Course Hold works perfectly, but it's inconsistent. Anyone else seen this? Any known fix?

Thanks so much!!