I only noticed the "enhanced AOR" bit in mine after reading your post

I don't know about yours but the subject in my email was like two lines long, so I'd have never noticed. I mean, look at this:
"Immigration, Refugees and Citizenship Canada - Communication to client/Immigration, Réfugiés et Citoyenneté Canada - Communication auprès de la clientèle - CPCM / CTDM - Enhanced AOR for Back Office".
Anyway, I replied to yours or someone's post in that thread that I doubt it has anything to do with actually missing documents because the very first line in the AOR is that it's an automated message. Based on CIC software used in other areas of processing, I find it very unlikely that it's sophisticated enough to let the people going through applications to send "automated" receipt messages but still allowing them to have some control over other parts of the message to indicate specific concerns. I think they just mean the police certs, medical reports and such.