We have exactly the same problem in two installations:
We have a new installation with a NMEA2000 network. In addition to all the navigation instruments, we also installed a Victron Cerbo and a Garmin Boat Switch.
As soon as we connect the Cerbo to the NMEA2000 network and turn on 'send data', the buttons on the plotters that control the Garmin Boat Switch will flash irregularly. The Boat Switch can no longer be operated. If we turn off 'data transmission' on the NMEA2000 network, there is peace again and the Boat Switch works fine again.
So it appears that the Cerbo and the Boat Switch are having a conflict on the NMEA2000 network.
