Thanks for your reply. I have configured the WS500 exactly as you have indicated. At the moment I cannot reconfigure the WS to set the shunt backwards because I am not on the boat till early march. But I am pretty sure that the purple and grey current sense wires have been connected correctly (purple closest to the battery; grey closest to the alternator) - see the wiring diagram that I made as preparation for installing the system. If you see something wrong, please tell me - thanks!
In the mean time, I also got a reply from the Wakespeed TechSupport : "The data that is displayed on the Cerbo is valued by Victron, not us unfortunately. I’m expecting this to be changed in a future update. " So they point to Victron, but you managed to get the communication with the Cerbo working, so I am still wondering which device should be looked at.