(wrong-type-argument listp #("Test document" 0 13 (:parent (#1))))
org-element-set-contents(#("Test document" 0 13 (:parent (#0))))
I was able to figure out that the error only occurs when I have an org file with document data, e.g. a line like:
#+TITLE: Test document
When I remove that line as well as #+AUTHOR etc, then it exports fine. With that line it, it won't export to HTML, LaTeX, or text.