------------------------------------------------------------------------ org-latex-title-command does not honor the document SUBTITLE or %s substitution, and throws an error invalid format character %s.
Investigation showed that org-latex--format-spec did not have an entry for %s. Making the obvious change appeared to resolve the issue: #+BEGIN_SRC emacs-lisp --- ox-latex.el~ 2020-02-07 13:59:34.804141887 -0500 +++ ox-latex.el 2020-02-07 14:00:18.836895973 -0500 @@ -1586,6 +1586,7 @@ lang)))) `((?a . ,(org-export-data (plist-get info :author) info)) (?t . ,(org-export-data (plist-get info :title) info)) + (?s . ,(org-export-data (plist-get info :subtitle) info)) (?k . ,(org-export-data (org-latex--wrap-latex-math-block (plist-get info :keywords) info) info)) #+END_SRC Emacs : GNU Emacs 26.3 (build 1, x86_64-redhat-linux-gnu, GTK+ Version 3.24.13) of 2019-12-10 Package: Org mode version 9.3.4 (9.3.4-elpa @ /home/srobertson/.emacs.d/elpa/org-20200206/)