I am using a Chromecast with System firmware version 275994 and Cast firmware 1.56.275994 (from Device Information in Home app). It is on 5G wifi. Until recently, I have been able to cast successfully from an android tablet (on 2G wifi), from desktop computer (Ubuntu 22.04) running Chrome (2G wifi) and from my pixel 3A (5G wifi). All of these still cast successfully with the YouTube, PBS Video and Netflix apps. But now I'm having problems with The Great Courses app (they know about the problem and have not come up with any solution, which is why I'm asking for help here). All these devices stream the GC content successfully as long as I don't try casting to my TV. When I do, it seems to start normally, but a split second later, the video stops and all I see is a gray screen with the Great Courses logo. It started with just a couple of lectures, but now it seems to happen with almost all of them. Things I've tried:
1. Reboot the router/wifi base station.
2. Do factory reset of the Chromecast.
3. Try changing the wifi channel.
4. Try putting the Chromecast on 2G wifi.
5. Try uninstalling and reinstalling the app.
6. Try with an iPhone (and freshly-downloaded app).
Maybe the folks at Wondrium will come up with something, but it doesn't seem like Chromecast is a high priority to them. The fact that the failure always involves showing the GC logo implies to me that the problem should be "evident" at their end.