I went to a friend’s house and we poked around with his LG TV but were unable to work around connectivity issues. Some threads describe an issue with LG secure connections. We tried disabling this on the Plex server, no luck. In any case, the original setting was “Preferred”, implying that such connections should have been reliably downgrading to unsecured when necessary.
Eventually we gave up on the LG Plex app and switch to a desktop computer.
So far, the only smart TV app I’ve been experiencing well is the Roku app.