I’ve had a similar issue with my setup and can’t get ARC working outside my local network. I’m pretty disappointed with the whole malarkey to be honest. My Roon Core is on my business iMac and I’m not prepared to comprise my firewall security by fiddling with my router settings and opening ports that could be hacked. Not really sure what this was all meant to achieve, having a firmware update that then forces changes on a networks security protocols to enable the software to work with an app that is meant to control the developer’s own software……