In split_chapters(output = output, build = function(...) bs4_book_page(..., :
You have 11 Rmd input file(s) but only 10 first-level heading(s). Did you forget first-level headings in certain Rmd files?
the name message. In both cases, however, the html renders correctly. This is from the unmodified repo as of the first commit.
So, what has changed since then, if anything? Otherwise, I figure it's a configuration problem with the rendering toolchain.