Hi folks! I now came across another issue of the NX units. I have two cases where the unit restarts itself every 7-10 seconds when trying to access the maps DVD after an update.
They updated their NX (7S7T..) with SP5.3 in order to run a 2014 map, which do not run in an old firmware (system is telling "incompatible data carrier"). After the SP successfully applied, they inserted the new maps DVD which also updates the navigation software and after the system restart at the end of the update, the restart-issue begins.
Nothing seems to cure this, even reflashing the firmware, which makes me curios. So the issue does not seem to occure inside the HMI firmware.