Looks like location and some close-by electronics were interfering with the signal. Why it only affects the 5Ghz-1 is probably anyone's guess. Looks good now. Thank you.

Please please please get this fixed. I bought a 2nd new router thinking the first one had a defect. Now I think you need to fix this by a firmware upgrade. Anyone else having this issue with v3.6???...

@Tony Hopefully you'll have a firmware update for the C4000 v3.6 soon. I've tried 2 different brand new routers and cannot see the 5Ghz-1 SSID showing up anywhere. Tried resetting and choosing...