Archer C7, 802.11r and iPhone stablity

I've got two brand new Archer C7 v2 (online, approx US$55 excluding shipping) and loaded with the latest LEDE Reboot. Configured for 802.11r roaming and using Android phone apps, I can see the FT is enable, and roaming is working fine for my Android phone and Windows 10 devices.
However, I have been told that the wifi has been unstable for my other family members using iPhone and other notebooks. Sometimes they have to either disable the Wifi or reboot the iphone to connect to wifi again.

I have left the channels and power as AUTO but I'm now considering locking them down. What else could I do to improve the iPhones stability ?

Anyway, 802.11r is a good reason to upgrade to LEDE if there is ever one... Picture of a file transfile on Windows 10 to a NAS over Wifi while walking around.

may have something to do with apple deciding that 'the standard 802.11r' wasn't good enough and teamed up with cisco to build some special sauce.