Thanks for the help
I made the test that you recommended and with online maps, and the position was correct.
I reimported a piece of IGN maps , same procedure as the first time ... and now the position is correct !!
the problem is for sure related to the maps generation , but I don't understand why (error on 2 differents types of maps IGN and OSM ),
now it is correct ... !!! that's good enough !!
thanks for your quick answer