Set the WiFi channel width to 20MHz (NOT 40MHz). It is a well-known issue that Apple devices don't work well with 20MHz.

Also, like @blacktubi said, if you live an area crowded with Wireless AP (especially in high-rise), you may want to consider 5GHz or better still, invest in HomePlug technology which is exactly what I am using.

I have been experiencing problem with my Unifi 30... wifi connection suddenly loses internet. HyppTV still continue playing. I plugged in LAN to laptop, there's internet! but Wifi on 3 iPhones doesn't have internet connected. Earlier I thought it was the stock router's problem (it was happening like every 1 or 2 days), so I changed to TPLink TL-WR1043ND. And I encountered the same problem again. I needed to restart the router to fix it. Has anyone experienced this? Any advice on this?