I’ve got a layout frame chain of music frames, the chain containing one flow.
I want to move one music system from the top of frame 3 to the bottom of the previous frame (page).
Manually compressing the staff spacing in the earlier music frame to create space I expected the flow to automatically reallocate itself and fill the newly created space. But it doesn’t; it’s as though the allocation of music text to frame is somehow locked and doesn’t automatically “trickle down” to fill space made available.
I’m stuck here, baffled.
Maybe I’m not expressing myself well here but this is the best that I can manage. 
Can anyone suggest what I should look at, what I should poke ?
Perhaps you should zip up and attach the Dorico file (or enough of it that we can see the problem). That would be a great help.
Big D, do you understand how to use frame breaks and “Make Into Frame”? That sounds like the solution here.
Add a frame break at the top of frame 2. Add a frame break at the beginning of the second system in frame 3. Click on the first frame break, and in the properties panel, toggle “Wait for next frame break.”
That’s magic! Vielen Dank – Kærar þakkir – Many thanks! Problem solved.
Sometimes Dorico works in mysterious ways …
Glad it worked! But it’s not mysterious. If you need an explanation, let me know.
I think I understand. It’s just a feature that I’ve never had to use previously so it wasn’t part of my armoury
“Wait for next frame break” forces everything into that frame until Dorico encounters the next Frame Break. Same with system breaks.
That makes sense …