A family of Microsoft word processing software products for creating web, email, and print documents.
An important note from this document
reads that "You must correct or Ignore all errors found in the document before the readability statistics will display." Have you tried that?
I came to this thread completely frustrated because I wasn't getting that Read and Stats pop-up I was remembering from Word 10. After clicking one of those instruction links someone else replied to your issue with, I realized I had completely forgotten that you have to go through all the recommendations first.
Once you click on the "Spelling & Grammer" 'button' or icon that you added to your ribbon through File>Options>Customize Ribbon, a 'Editor' column should pop-up on the right hand side of your workspace. This 'Editor' contains every suggestion Word has for your document. You need to ignore or correct every single issue listed under both the 'Corrections' and 'Refinements' headings before Readability stats will display. Every number must be turned to a green check mark. Readability statistics will automatically process and display as soon as you correct your last issue.
Another note, you might have to go back to sections previously corrected. I just went through this process for an entire novel. As I worked through the headings, I would complete a section, move onto another, and then suddenly find that the previously checked section had gained more issues.
Hope this helps someone! ♡