Looking at your traffic image, the target is 5700km away. Based on your location in the UK you're about 5700km north of lat/lon 0/0. I think the SkyEcho isn't sending ownship position so the script never updates from the defaulted 0/0.

Uncomment lines 136 and 138 so it prints ownship lat/lon and altitude. #print(ownship.latitude , ownship.longitude) #print('baro altitide:',ownship.altitude)

The NMEA protocol which XCSoar accepts relies on relative bearing and distance which requires an ownship position to calculate. Is your SkyEcho outside? It could be that its not receiving a GPS signal. You'd never know using other software because all EFB programs using GDL90 locate traffic with absolute lat lon.