I have a Philips TV that I usually use to cast from Plex, but it hasn't been working for probably over a month now. I have the latest firmware updates for the phone and am running the latest version of Plex. I can cast to an external Chromecast device and to a Firestick, but the Google Cast built into the TV just keeps showing the Plex logo with the spinning loading icon. Eventually I get a message "Unable to connect to TV". Generally a few minutes after failing, when I've given up and gone to another source, Plex will try to connect again which tells my TV to go back to the Cast input, but Plex still fails to connect.
I've tried with a wireless network as well as with a wired connection, and the Plex server is on the same network as the TV.
I've tried unplugging the TV for a while and plugging it back in - same with the network. I haven't changed any hardware between when this used to work and now.
I've also tried connecting from my android phone as well as from the web app.
Device: Philips 6000 series Google Cast Ultra HDTV
Model number: 55PFL6921/F7
Description under "Connect to device" in Plex: Philips UHD 2016 CastTV
TV Firmware version: PHL-0G0IU_227_0
Cast software version: 1.21.75378