GTK 3.24.48 is the latest GTK 3.x release, and it is the first one done using the new tag-based release process.
In the course of doing so, we discovered that it requires release tarballs to use the same name as the project, which affects their final location on download.gnome.org, which is now
https://download.gnome.org/sources/gtk/3.24/
(notice, no ‘+’ in the directory name).
Future GTK 3.x releases will use this location as well.