This is a new "thing" I noticed in the past 2 weeks. It happens 100% of the time. If you choose the Player Experience option as your Overseer reward, it will mention that you'll get X % of regular experience, and X % of a Merc AA point. Not talking about selecting the other Merc AA option. Absolutely 0 Merc AA experience now. 100% of the time, over many days of playing the past 2 weeks.
Not new. You need the merc out as said above. I thought they had said the xp for it was being taken away since they really meant you to choose merc xp tasks for that. But they haven't done it.
Also, the mercs have a limited buffer of AA points (I think it's 20). Once that is full, you don't even earn a % of a Merc AA point.
I have to correct my last statement - the Merc AA buffer is indeed limited to 20 points but you can fill the Merc AA % bar to max (100.0%).