I’m sorry it’s been almost a week until we got a chance to get back to you. We’d love to help find a solution to this connectivity issue.
Could you please check that both your Roon Core and your remote are running the latest version of Roon (Settings → About)? Also, is your iPhone connected to the same network as your Core?
Finally, if you have an antivirus or firewall, could you please temporarily disable it? Does the iPhone connect then?