Buttons across book documents not working

I've been creating buttons for years that link to a hyperlink destination in a different document in a Book and they've worked fine when exported to an interactive PDF. This latest Book (nearly identical to previous successful Books I've created) only has functioning hyperlinks/buttons whose destinations are in the same document, not across documents in the Book.

"Previous view" button works fine.

Something is broken when clicking in PDF on hyperlinks jumping to another doc within the book.

Table of Contents works fine.

A pretty simple 6-doc book with nearly all hyperlink destinations hyperlinks and buttons, not complicated content or appearance changes or anything.

Using the latest version of CC.

2 editors editing on a shared server at work (will try packaging to one of our desktops to see if that remedies anything).