I also ran into “poor connection” problem with ARC a few times when using my iPhone with T-Mobile network since 2.0 release. Each time when the connection problem occurred, my mobile data network was running normal with good speed. How I resolved the connection issue is to perform a “Roon ARC” test on Roon core (i.e. on server’s “Settings” page). The connection problem went away IMMEDIATELY once the “Roon ARC” test shows Ready status. Each time when I had problem connecting to the Roon core with ARC, I used this method to clear the connection problem. It never fails.
I suspect there is a bug somewhere in the ARC code that is causing the connect issue with a bogus “Poor Connection” error message.
So far I’m not able to reproduce the bug with a specific scenario. And that’s the main challenge.