title: Table of contents blank
body: <p>I am trying to create a beamer presentation using R Markdown. Everything was fine until I updated the software to latest versions of R and RStudio. Now my Table of Contents do not appear (blank page instead) and the words "Section 1", "Section 2" ... etc appear above every Section title on my presentation.</p>
  
  <p>I tried with toc: true, toc: false, changing theme, even creating a new R Markdown beamer from scratch but nothing worked.</p>
  
  <pre><code>---
  title: "TITLE"
  subtitle: "Subtitle"
  author: "Guillermo Ortiz"
  date: "9-oct-2019"
  output: beamer_presentation
  theme: "Madrid"
  toc: TRUE
  ---
  
  ```{r setup, include=FALSE}
  knitr::opts_chunk$set(echo = FALSE)
  ```
  
  # Hello
  
  ## Goodbye
  
  Bla bla bla bla
  </code></pre>