Ah ok. I see what’s happened.
Basically your music frames are all MA (Master) so Dorico is going to try to place each flow on a page, in the order that the flows are written. If you go into Galley View (bottom right corner of Write Mode) you can see that your actual music is in flows 1, 2 and 3; NOT flows 1, 6 and 10. This is why when you deselected flows 2-5, 7-9 etc. your music got deleted.
You’ve got two options:
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Cut and paste the music from flow 2 to flow 6 and from flow 3 to flow 10. Then untick as before.
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Cut and paste the music from flow 2 to flow 6 and from flow 3 to flow 10. Then go into Engrave mode, turn the Frames switch on, and in the top left corner of the first music frame click the drop down next to where it says “MA”. The “unlink”. Then click the dropdown next to “Flows:All” and just tick the flow that you want to appear on that page. Rinse and repeat for the other music frames.