Do you have any firewalls or antivirus applications running on the Mac? I’ve seen programs like Little Snitch, Bullguard, McAFee cause connectivity issues. Do you have any VPNs active on the iOS device? Are the iOS devices on the same network subnet as the Core?
Open Roon on the other PC you wish to try as the Core
Roon Settings → General
Disconnect
On the “Choose your Core” screen, press “Use this PC”
If asked to Unauthorize, you can go ahead and do so. You are limited to one active Roon Core at a time but you are free to switch between them as often as you’d like.
Verify if the same behavior occurs on the different PC