My 925 does that periodically with my Draytek router, usually a reboot of the router fixes it though. Probably the router in my case as it disappears from my laptop at times as well.
Wifi Tool/Analyzer cant detect anything at all.
I just reset my phone. It was updated to the latest version.
Even after reset it to ? 10.0.10586.107 still no wifi 5 Ghz. ( I planned to reset it to factory settings)