The white-on-login was the old Dashboard/Lobby installer's leftover autostart
relaunching the dead old URL (404 -> white), not a network race - so the
wait-for-URL launcher solved the wrong problem. Go back to the plain direct
Edge kiosk shortcut and clean up any stale launcher file. The real fix (the
legacy HKLM Run-key + old .lnk purge) stays; it just has to be published.