I got one of those emails, and online saw one of those "in the future" activity lines, with a bogus flight number. AA rep said that that was how the system marked activity that was still in process, and I should wait a few hours for everything to be sorted out. Which it was.

In my case, it was a deduction of miles for an foreign airport miles-plus-copay upgrade which cleared at the gate, and finally triggered the email and online activity 2 weeks later.