Update: So this may be totally anecdotal at this stage - I've not done enough testing to be 100% sure, but with today's OSX 10.11.4 update and iOS 9.3 these devices seem to be able to connect both much more reliably and the first time after restarts or quickly switching off and on wifi.
Is anyone else who has updated OSX/iOS seeing the same?
Running latest f/w? If not check the release note. We only have a MBP and couple iPADs using this router. No issues. Plus many Windows 7/10 desk tops, laptops,wireless surveillance cameras, two wireless printers, Synology NAS... All works fine. Wireless range is definitely improved with this router. Most notably on HTPC 5GHz signal strength was 60 - some db. always. Now it is below 60 db always. 2.4GHz is even better.