Tassilo,
You are correct; that was not the cause of the problem; I wrote you all too early. In fact, after lots of experimentation, it appears that if I try to load-package auctex in a standard emacs server (that is, after loading my init.el file), things fail as described above, while if I load it in an emacs -q session, everything works properly. I can definitely reproduce this behavior. So my environment is now where I want it to be. But if you want more information (such as my init files), I'm happy to provide it. I'm also now using 29.1 rc1 to fix the SVG bug.
Thanks,
Roger