It’s a known behavior that Dorico only “selects” what is visible, so it won’t copy paste anything that is not selected. It’s a good idea to select stuff in galley view with signposts on!
Normally I agree, but you can see what a mess the signposts make…
That’s why you need to set up a shortcut to toggle the signposts appearance on and off!
See also this recent discussion on the topic: