Maven's invitation Activation failed. You have not collected enough bosses in this atlas region

Zana mission doesn't count.

When you open atlas, there is circle in middle, cross over with mouse and you'll see with whom you fought. Those who are white (I mean on name of bosses), they are done, those who are like gray you have to fight with them. You can't call Maven bcs she already witnessed that map boss. If you don't have that circle, than play again only maps on which you can turn on Maven on map device, and you'll unlock it. When you have boss at Zana's, it doesn't count for Maven.