Hi Benjamin
A few possible theories come to mind, since InDesign doesn’t just decide to drop Parent content for the fun of it:
Parents not carried over when combining docs If they used the Book panel (File > New Book), when synchronising or replacing documents, Parent pages don’t always travel with the compiled file the way styles and swatches do. It’s possible those four double spreads were defined as Parent in one component file, but when the compiled doc was made, those parents weren’t imported. In that case, the compiled file would create new blank parents (often just A-Parent) and the page numbers/headers vanish.
Pages re-assigned away from the parents Sometimes when you replace or shuffle parent pages in a document, the pages can lose their parent assignment. If the compiled document didn’t know about those parents, the spreads might have been reset to “None,” leaving the text frames gone.
Section markers or variables instead of static text If the chapter titles were controlled with section markers or text variables, they might appear blank if the compiled book file didn’t preserve the sections properly, or if the sync wiped out the variables. That would make it look like the content “disappeared,” when it was really a reference that got broken.
Corruption or odd parent-page overwrite In rare cases, if the user had identical parent names across multiple docs (say four different “B-Parent”s), then when the files were compiled, InDesign could overwrite one with another, leaving them empty. That could explain why it only hit those four spreads.
Viewing mode / PDF preset Less likely, but worth ruling out: if the PDF export preset excluded non-printing objects or layers, and the parent text was accidentally on a non-printing layer or hidden layer, they’d vanish in the PDF. But since they said the compiled doc itself looked empty, that seems secondary.
A few questions
Did you create a Book file or merge everything into a single INDD?
Were the parents uniquely named in each file?
Were the titles static text or driven by markers/variables?
In the compiled doc, if you check Pages panel, are those spreads still showing a parent applied or set to None?
My hunch: Parent page names collided during compilation, so InDesign kept the blank ones and discarded the designed ones.
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