Now I have tested BIOS versions 0041, 0042, 0045, 0047 and 0048. No success. In every version the same issue. I have tried a number ofdifferentBIOS settings with no success. Even if the LAN adapter is deactivated in BIOS, the LAN-Port is still active.
During mytestsIhavefound out, however,that the LAN-Port is inactive for one second while the NUC is shutting down. After that second the LAN-Port is re-activated.