N66U Can't connect to 5GHz

[dgwx]

This worked fine for a long time. Sometime in the last few days I have not been able to connect my phones at 5G. They were both connected at 5G before. When I bring up the list of wi fi networks the 5G network is listed as "not in range". This is happening as I am sitting about 2 feet from the router. I have 3.0.0.4.380_3831 installed on the router. I was still able to get a 5G after installing this version.
Its possible, but I am not sure, that this started after I set up a 2.4 guest network for some connected home devices. These devices do not run at 5G.
What can I try to get 5G visible again so I can connect to it.

 

[dgwx]

I don't know whats going on, for several days my phone could not see the 5G network, this morning it could and I was able to connect.

 

[radekker]

The same here with me.
Sometimes the 5G network simply disappears from the air and my phone reconnects to the (slower) 2.4G network.
I went back to fw 3.0.0.4.380_3264 for that reason.
No issues since the last 24 hours and the 5G speed seems to be fine.