Stream on Mac OS goes blank when connected to external monitor

It all started a couple of months ago. When I use an external monitor on my Mac running Monterey I get sound from the DirectTV Stream, but no video. If I unplug the docking station the video will play on the laptop screen. If I plug the docking station back in the video plays on the external monitor correctly for about 10-15 seconds and then goes black, but I can still hear the sound. I've tried changing he HDMI cords to ones I know work. It only happens with DirectTV, other video streaming work correctly.