I have this same problem. Trying to cast from Fedora to a Philips TV and it showing error after some time. My logs also include the ‘codec list not initialized’ warnings:
❯ flatpak run org.gnome.NetworkDisplays
(gnome-network-displays:2): Gnd-WARNING **: 20:09:42.275: NdCCProvider: Failed to resolve Avahi service: Resolving failed: Timeout reached
(gnome-network-displays:2): Gnd-WARNING **: 20:10:25.818: codec list not initialized
(gnome-network-displays:2): Gnd-WARNING **: 20:10:25.818: codec list not initialized