I agree its unlikely to be the gauge earth connection Mark as its common with so many other unaffected circuits hence my suggestion of breaking then re-making the VDO connector which carries CANBUS high and low lines among others. Fingers crossed that fixes issue.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone