Adobe Illustrator can show an odd behaviour when you click on the workflow menu inside the PageProof add-on. This is a known issue to Adobe with having User Interface Scaling turned on in your Illustrator preferences (this is a default setting but should be changed).
To fix the workflow drop-down menu
Turn off the UI Scaling in your Adobe Illustrator Preferences. Click Preferences, then drag the slider for UI Scaling to Small.
This will now make the Illustrator interface the same size as all of your other Adobe CC applications.