It’s nothing to do with the extra pages.
In your original “Test” file, the first bar rests are all explicit (you’ll see them as black rather than grey if you go View > Signposts > Implicit Rests).
In your “Test 2” file, none of the rests are explicit; they’re all grey.
In your original “Test file”, if I “Remove Rests” on the first bar, Dorico automatically recognises that the second bar’s rests must be made explicity (which you can do manually by selecting and hitting O to turn on Force Duration).
For some reason that isn’t happening in your “Test 2” file.
All you need to understand is this:
In order for Dorico to be able to remove rests, something explicit (whether a note or a rest) must exist somewhere on that stave, in that flow. It could be a single note at bar 763, or it could be a single bar rest at bar 1289 that has been made explicit by you selecting it and typing O.