Thanks for your work with Calibre Companion. I've found it a useful tool connecting to Calibre on my desktop (MacOS) using the Content Server approach.
I recently changed to storing my library on a local Ubuntu Linux network server using calibredb and calibre-server. The library can now be accessed using a browser from a mobile device on the local network ; e.g. (static lease)
http://192.168.1.21:8080. But not from CC. Connection attempts always end with the "Cannot connect" dialog. Entering the IP Address and 8080 port manually results in the same.
Ironically, connecting to the MacOS Calibre Content Server will work while its library is on the same local Ubuntu Linux network server that CC will not connect to directly.
Any troubleshooting suggestions appreciated.