How do I stop automatic double break tags in ckeditor?
The answer in this post helped me out:
CKeditor adding an extra &lt;br/&gt; tag when a &lt;br/&gt; tag is encountered

basically go into
administration > configuration > content authoring > text formats. 

then select the text format that's causing problems and unselect "convert line breaks into html" and save configuration. 

Then clear all caches on Drupal and browser. The content should go back to normal just by visiting the page while you are signed in otherwise saving over it should fix the problem.