iPhone 5S + N66U WiFi Issue

[Poseidon]

I'm hoping to find a solution to a strange issue. My sister has an iPhone 5S and she connects it to her RT-N66U router via 5GHz wireless.

She has separate SSID *and* passwords for 2.4GHz and 5GHz but her iPhone keeps bouncing from 5GHz and connecting to the 2.4GHz randomly.

In settings, she deletes BOTH wireless profiles and connects to the 5GHz wifi only - but a few hours later, her phone automatically connects to the 2.4GHz.

Anyone know what is causing this and how to stop it please?

 

[bluepoint]

The 2.4 GHz band has a longer range than the 5 GHz band. Because of that wifi clients(iPhone5s) will connect to a stronger signal when both profiles are present. If your sister's iPhone 5s still connects to 2.4GHz band, it only meant the 2.4GHz profile was not completely deleted. Just tell her to just start over and reset the networking settings then start connecting to the 5GHz only.
Note: This procedure will erase all profiles in the network.
Settings-->general-->reset-->reset network settings