When using the AGL doc site from a mobile phone the Table of Contents is presented as a pick list. Choosing most of the sections from the pick list will result in a 404 error. This can be simulated in a desktop environment by making the browser window narrower than usual.
For example, if you browse to
Then narrow the window so the TOC pick list appears, if I select "Preparing Your Build Host" and 404 error is returned.