After first 30 min ride, the radar gauge seems to be working. The color bar showed the speed and number of cars behind me and it worked the whole ride time.
I am just back from a 53 km/ 2 hours ride.
FR 955 is on firmware 30.31 and during the whole ride the gauge was working as expected on a static screen. Radar symbol was always visible and the gauge appeared as soon as a vehicle was approaching and showed the distance.
Fixed for me, thanks.