Whilst I feel fortunate to have missed out on these problems in only buying after the first big batch of firmware and software updates I've still been struggling with the 5Ghz band Wifi issues; that is, until now.
Basically I've had WiFi problems with Windows Phone 8.1 and Surface Pro 3; although not Surface Pro 1 funnily enough. A registry hack enabled visibility of 5Ghz networks on the SP1 but after recent WP8 updates I've not been able to acquire those networks any more. 2.4 Ghz is fine, and if separated from the router by more than one or two solid walls (esp. re-enforced concrete) 5 Ghz is next to useless anyway. I'm not going into details here but you can read about it on StackOverflow if you're interested.
However 5 Ghz is great for the same vicinity plus network storage / high data transfer, which is why I'm interested in getting it working over our home network. After two weeks of frustrated router settings experiments I found the solution whilst browsing with my Saturday morning cup of coffee.
The answer lies here on the Windows 8.1 Forums over at Microsoft. Now whomever UKNOWJP is, they deserve a medal - it only solves the problem on networks where you have privilege to change the router & AP settings but on your own network it's a winner.
There's all sorts of answers on the web about deleting drivers, updating router firmware, messing around with recovery partition driver versions....all valid solutions to other specific problems. However across all the different devices and patch versions I found across the forums this one was unique in that it solved the initial problem.
Just change all 5 Ghz networks channel numbers to below 100 - channel 36 is suggested in this post (you still need to use different channel numbers for different networks on the same frequency).
Don't forget: Reboot the router after you've logged in to the admin area and changed your settings; this prevents any possibility of latent session capture by unwelcome guests.
Now Windows Phone 8.1, Windows 8.1 (SP3 and SP1) all see every single WiFi network our routers provide...but it's not a silver bullet.
Prior to this I hadn't altered the channel number on the 5 Ghz networks so above channel 100 was the default setting. If that's the case we cannot guarantee that all networks of this frequency will enable contemporary Windows devices to connect - this only appears to be a problem with AP's running the 802.11ac protocol afaik.
Overall I think Microsoft need to work on some updates which don't have this channel number requirement - and disclose why this problem exists.
Addendum: I haven't checked this with iPhone yet, my better half has a 4S - that and iPhone 5 weren't 802.11ac capable...Will update when she gets her iPhone 6 to see if these settings are compatible.
