Yes now it works normally !!
The solution was simply to unplug the in-car charger.
The difference in signal strength can be easily seen using “GPS test” app : signal bars are divided by 2 when charging and some satellites disappear !
I tried with a randomly chosen ferrite bead on the charging cable but it is the same.
Using an USB port of my battery-powered laptop gives the same result.
Can some of you do the same test with “GPS test” app and tell me if they see the same attenuation in signal strength when charger is connected ?