hello JacquesV.
im sure the moderators-masters and experienced users will guide you through your problem.
i also have an android head unit, with igo luna skin by pongo many years now ... (gps antenna in the middle of dashboard). never had so much delay and response time on route... maybe under bridges or inside tunnels.... my opinion is sys settings and head unit settings.. (igo apk all rights- clean install etc) i will follow your post .. wish you the best solution!