Navigating "Book of Vaadin" -- No more TOC?

What happened to the Book of Vaadin, with the online web edition?

I remember it having a long detailed TOC (Table of Contents) listed on the right side. Now that list is very short with only 2 levels of detail.

I cannot find any page with a detailed TOC. I found this page, but it is too short:
https://vaadin.com/book/-/page/preface.html

Is there some TOC I’ve lost track of?

The “Up” link at the bottom of the pages is useless. It displays a page with a header but no real content.

–Basil Bourque

Hi,

thanks for reporting this issue. The Table of Contents column is now fixed.

Yes, the TOC now appears on the right to 4 levels of hierarchy.

But the Up link, if I click it twice, takes me to this page without content (a minor issue):
https://vaadin.com/book/-/page/part1.html

–Basil Bourque