Loss of video out in Edit Tab only

Fairly new to Resolve and still learning all the ins and outs but I'm stumped. I'm editing and I've lost the ability to see my video on my external monitor. This is only when I'm in the Edit tab. All other tabs seem to work. I can playback just fine in the Color tab. The external plays fine but when switch back to the Edit tab the last frame the playhead was on in the Color tab remains on the external monitor and it won't refresh.

I am running on a 2013 MacPro and I have an external box with a Decklink card. I've rebooted everything but to no avail. I put in support help last week but haven't heard back so I thought I'd try the forums. It could be something completely idiotic, a setting that I inadvertently clicked on or triggered but I'm stumped. It happens on any project that I load.

thanks

Phil