I've been having issues with my Arris Surfboard SB6900AC lately and decided to upgrade to separate modem/wifi router. I got a nice Netgear Nighthawk XR500 (works great, very nice), and a CM1200 modem to handle modem duties for my Spectrum service. My issue is that the CM1200 will lock 31/32 of the downstream channels, but only 1/8 upstream channels. The downstream and internet lights are solid green, but the upstream will continuously flash. No internet access. I had a Spectrum tech come out to inspect it, and no issues were found except a mildly leaking coax connection (replaced). Any ideas?