The tutorials links were recently missing when I changed hosts.
To make it easier when I update articles, I have all the links for a tutorial series in one file that gets included via php.
My old host, I wasn’t able to use relative links, so used absolute HTTP links. My new one (with default php settings), disables absolute include links (HTTP), which seems to be a security issue (someone could hack you page and have it include a php file from their server).
So, I went through, and they should all be updated and linking correctly (showing all parts in a tutorial series, at the end, and under the tutorial category page).
Hope that makes it easier to go through a tutorial again!