title: Blank elements and issues depolying Shiny/Flexdashboard with R Studio
body: <p>I am working on a simple dashboard with using R, Shiny, Flexdashboard and Leaflet. The code itself seems to work fine. However I am facing some issues to deploy it.</p>
  <p>When I run/Knit the document for the first time everytyhing seems ok, but if I try to publish it I receive this message when I hit the 'Publish' button above the rendered document:</p>
  <blockquote>
  <p>'Only rendered R Markdown documents can be published to RPubs. To
  publish this document, click Knit to render it, then click the Publish
  button above the rendered document'</p>
  </blockquote>
  <p>Then, if I reload the page or Knit the document again without make any change, the tables and the maps disappears.</p>
  <p>Initially, I thought it was something with Leaflet, but I got the same behavior with this minimal and reproducible example both in R Studio and R Studio Cloud.</p>
  <pre><code>---
  title: &quot;Example&quot;
  output:
    flexdashboard::flex_dashboard:
      orientation: columns
      runtime: shiny
  ---
  
  ```{r }
  library(flexdashboard)
  library(shiny)
  library(DT)
  
  # OPERAÇÃO POR BAIRROS
  link = &quot;https://docs.google.com/spreadsheets/d/e/2PACX-1vS3cj3PhVm-2F-CiEJOE8O1YIIU6t7os_wDDrACFne39ZRUvxLKdV_MKZNzD6xTG0hoI5ZroHpxyIzV/pub?output=csv&quot;
  df_op = read.csv(link)
    
  ```
  
  Column {data-width=350}
  -----------------------------------------------------------------------
  
  ### Table
  
  ```{r table}
  
  df_table = reactive({
     df_op
  })
  
  DT::renderDataTable(df_table())
  ```
  </code></pre>