Yup, same here. Since at least 8.6.0 and continuing with latest beta from 15 Sep 2020. See here: Chromecast Ultra and 2nd Gen - Error code: h4 (Not Supported) for another report. Though I suspect it has more to do with the Plex for Chromecast being updated recently than the Android app.
Like you, disconnecting from Home works fine. Likewise, loading another app to Chromecast (e.g., Netflix) and then disconnecting from that also works.
@bigwheel: looks like we have another bug here. Please acknowledge.
