I've got an iPad Air and an ASUS RT-N66U router. (On Plusnet FTTC BT).
Connecting on 5GHz it is fine for the odd web page or so, but within minutes of starting to stream video it clogs up then very soon after it hangs (on the video) and doesn't want to know until you restart it.
On 2.4Ghz it is perfect.
I assume the problem is with the iPad, as I don't need to touch the router.
My broadband basic info/help site - www.robertos.me.uk
| Domains,site and mail hosting - Tsohost
Connection - Plusnet
UnLim Fibre (FTTC). Sync ~ 57.1/14.8Mbps @ 600m. - IPv4BQM
"Angels can fly because they can take themselves lightly."
- G K Chesterton.