I'm having this same issue right now. It happened out of nowhere. I don't have any playback in the fusion page. But any nodes I add (like blur) will playback fine in the edit page WITH the effect. It's happening with adjustment clips, fusion clips, and even the original clips itself.
Using DVR Studio 19.
EDIT!!!!:So I'm pretty sure I figured out what's causing this issue.
I was looking around the forums and tried several solutions until I found :
https://forum.blackmagicdesign.com/viewtopic.php?f=21&t=159464After changing the fusion settings, I restarted DVR and I now have playback in the Fusion Page.
That said I also have to add that I changed another setting at the same time so that also could have been the solution. I checked (enabled)
- Use gray background for user interface.
- Use gray background in viewers.

I had these enabled before but disabled and enabled them while trying to solve the issue.
Not sure if this is a bug or if I was doing something wrong but I'm glad I fixed my issue since I've read that some users had reset their OS in order to fix the issue.