How to render citations inside a beamer subtitle in Rmarkdown?

Question

I'm trying to combine both adding subtitles to beamer frames and rendering citations inside them in Rmarkdown. In LaTeX I've been able to do this with the following code:

\begin{frame}{Kontrastive Analyse: Russisch-Deutsch} 
   \framesubtitle{Phonetik und Phonologie kontrastiv: Russisch und Deutsch \parencite{kuemmelPhonetikundPhonologieRussischundDeutsch2017}}
...
\end{frame}

However, I'm having a hard time doing the same in Rmarkdown, where I have the bibliography defined in the YAML on the one hand and on the other hand also defined in the custom tex header.

So far, I've explicitly written the frame subtitle as LaTeX code (because I currently don't know how subtitles can be made in Rmarkdown beamer format; pipe character doesn't seem to work) and within the subtitle code use biblatex's \parencite{}, as follows

\framesubtitle{with a subtitle \parencite{kuemmelPhonetikundPhonologieRussischundDeutsch2017}}

So while the rest of citations written in markdown format (i.e. [@citekey]) are rendered without problem, citations within subtitles aren't. How can I solve this?

Here's the code so far:

---
title: "Presentation Title"
subtitle: "Subtitle"
author: | 
  | [Name]
  | \scriptsize [Email]
institute: |
  | [Institution] 
  | [Faculty]
  | [Institute/Department]
  | [Seminar] 
  | [Professor]
  | [Semester]
date: \today
output: 
  beamer_presentation:
    latex_engine: xelatex
    keep_tex: TRUE
    slide_level: 3
    includes:
      in_header: "myacademic-preamble.tex"
classoption: aspectratio=169
link-citations: true
bibliography: '/Users/marco-andres/Documents/Zotero+Pandoc/MyLibrary.bib'
csl: '/Users/marco-andres/Documents/Zotero+Pandoc/institut-slawistik-hu-berlin.csl'
---
\frametitle{Table of Contents}
\tableofcontents

# This is a dividing slide

## This is another dividing slide (subsection shown in TOC)

### Here's an individual slide 
\framesubtitle{with a subtitle (Kümmel 2017)}

# Bibliography

\printbibliography

The custom .tex relevant for LaTeX-style bibliography is:

%Bibliography and language
\usepackage[english]{babel} %section and bibliography langauge
\usepackage{csquotes}
\usepackage[style=authoryear, sorting=nyt]{biblatex} %bibliography style
\addbibresource{MyLibrary.bib} %bib file