Hi aapple83 ,
Please provide the exact dot version of the software & OS installed at your system .Also check whether is there any update available for the software after going through "help > check for updates "
Follow this thread to reset the preferences for the Acrobat software :- How to reset Preference settings in Acrobat.
Then open Acrobat, navigate to Help menu & repair the installation.
Would like to know is this happening with all the documents or with certain one .
Please check with application used in creating the document.
Please refer to this KB article :- Page thumbnails and bookmarks in PDFs, Adobe Acrobat DC
Let me know if it works.
I'm on Adobe Acrobat DC version 15.006.30121, running on Windows 8.1 Pro.
This has happened on several different documents and to multiple colleagues of mine.
The documents are created by printing to PDF in Microsoft Project 2013.
Please check with the above suggested steps & articles .
Let me know if it works