Diagnosis
The TV's wireless module has weak reception or a driver issue. It cannot see certain 5GHz channels.
How to Fix It
Log into your router's settings. Change your 5GHz WiFi channel to a lower one, like 36, 40, or 44. Save and reboot the router. Then on the TV, go to Network > Wi-Fi Connection and scan again.
If That Didn't Work
The TV's WiFi antenna connection inside the cabinet may be loose. This requires opening the TV to check the white antenna cable connection on the main board.
Heads Up
Some routers use DFS channels (52-144) which this TV often cannot detect. Stick to standard channels below 48.