Thank you! \hspace* works great.
In fact, this has nothing to do with pandoc, but is a known behavior of LaTeX:
See https://tex.stackexchange.com/questions/318454/quad-not-working-after-using-newline.
Suggested solution: Use `\hspace*{2em}` instead of `\qquad`. (Do use the starred version, otherwise this will not work.)