I had this same issue (No Network) when attempting to upgrade from stable 6.9.2 to RC8. I have two NICs (USB and PCI).
I copied my network.cg and network-rules.cfg files from my USB backup however after booting network-rules.cfg is missing again. I tried this several times and then gave up and downgraded back to 6.9.3 for now.
Let me know if I can help provide any additional info etc. ?