Does Roon ARC work when connected you WiFi in your home so that it is on the same network as the Roon Server?
If it does you need to post the diagnostic text from the Roon ARC settings page of a normal Roon Client (not ARC). This will likely tell us more about what is going on.
If ARC does not work when connected to your home WiFi, then you could try, whilst connected to your home WiFi, going to ARC settings, scrolling to the bottom and selecting ‘Disconnect from Roon’ and then logging in again (note: I believe all your ARC downloaded files will be removed when you do this).
If that does not work, then you could try uninstalling ARC and then reinstalling it .