Streaming error TVAPP-00236 - unsupported display

I have been using xFinity streaming successfully for years, and suddenly I have a problem today.  My setup has not changed, I have not installed any new software, there have been no changes to my network.

I have a MacBook Pro (2019), running Catalina 10.15.5

Running Safari 13.1.1

External display is a Cisco DX80, connected via (genuine) Apple display adapter and HDMI

When I try to stream content while the external display is connected, I get error code TVAPP-00236, with the message that my display is unsupported and I should connect a supported display or use an Apple display adapter.

I have rebooted both the MacBook and the DX80.  I have plugged the display adapter into each of the four USB-C ports on the Mac.  I have tried another Apple display adapter, all result in the same error message.

Hmmm, well, this display, in this very same configuration worked just fine yesterday (and for a couple of years), and I AM using an Apple display adapter.

Streaming works just fine if I disconnect the display (however, that is not ideal, since I need the display real estate.)

Thanks in advance for any insight into what might be happening here, and potential fixes.

Thanks!