I agree this sounds like a network/wifi config issue rather than a Roon issue. The fact everything else works for you sort of confirms it to be honest, if there was a Roon issue I’d expect other problems in your setup.
Could it be due to your wired and wifi networks being on different IP subnets? Is there a firewall/router/switch between the wired and wifi networks that is causing a problem? I had to turn off IGMP on a managed swtich in my LAN to get Roon to work smoothly for instance.
You should really raise this in the support forum, I’d be very surprised if it cant be fixed. Most users have no issue playing through their iOS devices myself included.