Do you have any other devices capable of connecting at 5Ghz? Can they see and connect to the network?
If so, it could be a issue with the fact that the Oppo r7 Plus is Wifi AC draft. Try setting the 5Ghz network to "802.11n Only" as seen on page 43 of manaul
Also, just to confirm, is it a Oppo r7 or Oppo r7 PLUS
? Main difference between the two is Wifi AC, which is the 5Ghz capability.