Thank you, Tom!
This solved it.
Now I know what that gray strip was - it was the empty main storyline and by converting the artificial gap clip down it made it all work again!
I had a few clips tacked on top of that storyline and the stayed in place.
PS:
This was another one of DaVinci Resolve's peculiarities. It is a great application - but I feel they are pushing the development so hard and so fast that some basic things break. (there's already a v16 beta on the horizon)
One of the real strange things of DaVinci is that what you see is not what you get on output- even if you upload a 3Dlut to correct the viewer and even though I changed the output setting from DVR's working gamma of 2.4 to the Quicktime gamma of 2.2., Images come out too bright. So I always have to do a correctional curve. I take DVR's output, open it in a Quicktime viewer, then define a luminosity curve, then check the output again.
A DVR guy would say I'd have to use a specific monitor, not the viewer on a computer display, but how many independent filmmakers have a 2000$ monitor just for that?
But color correcting in DVR is just so amazing which is why I'm going through all this - I feel I can get nowhere near that precise color and light mood in FCP that I can get in DVR in a short time. And the node system, where you can turn on and off parts of your correction is also great.
I just hope they will one day make their viewer show the same image as DVR outputs.