I have opened as well an issue for the pychromecast lib, since the upgrade breaks as well pulseaudio-dlna: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=965250
Not really related but also pulseaudio-dlna is not working for me even when downgrading to pychromecast v5: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=965251
