I have the NUC5i3RYK with the soldered-on Intel Wireless-AC 7265 adapter. I'm running Windows 8.1 with the latest Intel Wireless drivers (17.14.0).
It connects just fine to my AC router at the expected 802.11ac link speed of ~866Mbps, and shows in Windows Task Manager as an AC connection. The problem is when the NUC resumes from Sleep or Hibernate, the connection consistently drops to 802.11n and max 300Mbps link speed - and I mean every time. Reconnecting to the router doesn't restore the AC connection - only disabling & re-enabling the adapter forces it to quit N for AC. And there is no Advanced option to force only AC connections with this adapter, it seems.
As a workaround, I've noticed that this behaviour can be corrected if the following option is unchecked on the adapter: Power Management > 'Allow the computer to turn off this device to save power'. This is regardless of any Power Profile settings for WiFi.
Oddly, what this workaround seems to do is switch OFF the WiFi card completely on Sleep/Hibernate - because when resuming it can be seen in the tray first switching on the adapter then re-connecting to the router. With the power saving option checked, this doesn't seem to happen - the adapter doesn't cycle and doesn't force a re-connect to AC vs N. So perhaps the power saving option is just backward here?
Has anyone else seen this problem with this card on these NUCs?