I'm having this exact same issue with the xr500 and philips hue bridge. Over LAN, the bridge works fine. I can connect to the bridge etc, but with my iPhone, it will find the bridge but then not allow it to actually connect. Interestingly, if I use siri commands on my phone it will sometimes allow me to turn lights on and off etc.
This is a really frustrating issue that appears to be affecting more than just me, I'd love to be able to provide any further information or testing to help.
(I tried disabling QoS completely and had the same issue)