The PDF below has a Table Of Contents button in the top-right corner on each page that will send you back to the table of contents page. These page links strted working again after the last Yumpu update.
The issue now is that the characters in the top-right button are scrambled on some of the pages.
The Table Of Contents button in the PDF below does not work. It was uploaded to Yumpu a few days ago with the same upload settings as all other PDFs on my website. None of the page links in the Table Of Contents work either.