Netgear Wifi booster and iPhone hate each other

[Username32]

I have a Netgear cable router C6300bd in the middle of the home and a Netgear wifi extender EX6150 at the back of the house. The extender is set up in "FastLane mode" -  5ghz connection from main router to booster; then the booster broadcasts a 2.4ghz connection to devices in the back of the house. 

The setup works well - my Macbook and PS4 are connected to the wifi extender fine, no problems.

My iPhone 6 connects to the wifi extender OK.  But notifications are delayed.  And if I open Facebook messenger, it takes up to 20-30 seconds to connect. I've also had issues checking for new emails which takes forever. Sometimes it shows the "4G" symbol instead of the Wifi connected symbol.  The unreliability has forced me to use cellular data on the phone or try and connect it to the main router  (with a very weak wifi signal).

It just doesn't make sense - because the Macbook and PS4 run exceptionally well

I read somewhere that disabling QoS/WMM might fix the issue - but I can't see how to do this for the wifi extender  ?

Do I need to forward ports ?

Are there settings on the C6300 that I need to change ?

Any ideas ?

iPhone 6 running iOS 10.1.1

[Username32]

And even when the iPhone shows it is connected to the Netgear - full bars on the wifi -  it doesn't load stuff.   It's like it's connected but not  if that makes sense.

[DarrenM]

Hello Username32

Do you have you extender named differently than your main router if not the phone could be holding onto the weak signal from the main router.

DarrenM