Similar to a post someone encountered last year, I have a single contact (my best friend) who doesn't appear to show up in either the Outlook.com website or the Windows 8.1 People app.  All other contacts appear correctly, and this specific missing contact appears on my Lumia 925 correctly.  I've re-linked my Facebook account, which had no effect. 

I've reached out to this individual to see if perhaps he somehow "blocked" the Microsoft app in his FB settings (I noticed that "Windows Phone" is, in fact, a separate app)  Is there any diagnostic method available to an end user to determine the specific results of the API calls that Microsoft is making on their behalf that could identify if it is in fact Facebook not returning the data?