Enabling 802.11r (FT) leads to invisible network for some clients

Hi everyone,
I've set up my home network using two OpenWrt based routers, a mir3g and a wrt32x on a recent snapshot. I want to get 802.11r working to see if I could get improved handover when moving around the house. First of all, a great job on how easy it is now to configure.
Now after enabling the settings in LUCI, immediately my chromecast dropped off the network. Also I found my Linux based PC is unable to even see the network using 'iwlist scanning'. I've tested by turning 802.11r off again and the wifi network showed up again. Turn 802.11r on and it's gone.
Looking at the network using Android / WiFiAnalyzer, simply shows the network and the expected +FT.

Is this supposed to happen? I always assumed that clients not supporting 802.11r don't get negatively influenced. Just no fast transition.
Or do I need to configure something else I don't know about.


Any suggestions are welcomed!

Best regards

I know that in Android the network with 802.11r appears,at least, in a Galaxy Core 2 and Ace 4 Lite, but it does not recognize the type of security.

Yeah, here a OnePlus 5 and galaxy S5 can connect and interestinglya Chromecast cannot. Does this mean that we cannot enjoy 802.11r until all devices are replaced?
Or could the be a way around it?