> I only have one \book block in my case as I think I always do. As I > mentioned the file-1.pdf usually is accompanied by error messages > leading to a fix which eliminates the file-1.pdf but not in this case. > At this point it's just a nuisance not worth creating a MWE.
The other \book might be implicit as in
\book { { c' } }
{ c' }
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