title: pandas.DataFrame.to_csv not exporting all rows
body: <p>does anyone have an idea what could be causing pandas.DataFrame.to_csv not to export the complete dataframe?</p>
  
  <pre><code>print(len(df))
  [77814 rows x 42 columns]
  df.to_csv('filename.csv'))
  </code></pre>
  
  <p>The resulting csv files has 54470 lines and is missing block of data around 1/3 down the file. My data is time stamped to I can tell that the missing data is one large chunk and not random points throughout the file.
  I'm working in python 3.6.5 and pandas is 0.22.0.</p>
  
  <p>Thanks a lot for your help</p>