I received this email as well. I know I had an issue with the Marriott in Orlando. It took over 3 weeks to post. Upon speaking with Marriott Corporate, a select number of Marriott hotels were having issues posting points to the accounts. They issued me a courtesy point bonus at that time, so kind of surprised to see I received this today.

It was a known issue though, so you probably stayed at one of the hotels that had problems of posting points automatically. The hotel you stayed at though may have been smart enough to know they could manually post the points.