Newbie here. I installed Sonarr on 06/25/2020 (and Radarr on 07/07/20) and both were running fine. Now, I can’t access Sonarr by browsing to localhost:8989 (or localhost:7878 for Radarr). I initially had this problem and did the chmod +x command on both and that fixed it. It’s not fixing it this time. The only new thing I recall doing was a Catalina upgrade.
The folks on Reddit helped me solve my issue. I needed to add the Sonarr and Radarr apps to my startup items. Don’t recall doing that when I installed but that fixed it.