Update.
I was troubleshooting the NUC with the help of Intel Customer Support.
What I have done:
- I have installed Windows 10 on the NUC (I have to reformat the SSD to NTFS since the previous installation of Roon software has formatted the disk to FAT32. Thanks Google!).
- once Windows 10 installed, I have updated the driver of the controller using a USB flash drive.
- after rebooting the NUC, it was immediately connected to the router. Yeeaah!
- finally I reinstalled Roon software and all is fine.
A happy Roon user 