Are you simply editing the grub file on your USB or are you editing the image file then re-writing it to the USB stick?
I had some issues making direct edits to the grub file. It may be changing it in a manner that alters the file with characters or formatting you cannot see.
1. Redo the USB from scratch with a fresh image mounted using OSFMount and then edited using Notepad ++ as advised in the tutorial.
2. Download the spreadsheet (excel) for serial and MAC and create them (if you download it and make it editable it will redo the serial each time for you).
3. If you do not need "Quick Connect" just use your actual NIC MAC rather than the one from the spreadsheet.
4. Burn the image to the USB with Win32Diskimager or similar.
Also, have you changed any bios settings? Mine was being troublesome until I set it to EFI and cleaned up some of the options. I'm using a Supermicro server board though so my issues may not reflect yours.
If you are having issues I advise go back to basics and ensure you are not overlooking any simple aspects.
I am just simply editing grub file with notepad++ and save it on USB. I think that i have fix the problem by adding IP adress to fixed IP on my router so now my server is upp and runing for about 4 days. Please can you share link to spreadsheet (excel) for serial and MAC.