Oh I see. Since I had access to your instance for fixing the issue anyways, I saw that the app was healthy and running, but the nginx reverse proxy config wasn't correctly updated.
This may actually be a bug in Cloudron. The reason likely is that I've changed the app's internal port from 80 to 8000 to not require apache to run as root.
To fix this quickly, I've just submitted the location form of the app configure, which triggers a recreation of the reverse proxy files.