This one is simple, minor and I remember it from WoM.
The "Speak to" button gets greyed out if you click in any of the areas with info of that faction (sorrounded in red in the second pic). You need to change another screen or select another Sovereign in that list to "fix" it.
While the button is greyed out, it still works to double click on the Faction bar (to the left of the Faction detail shown in the pics) to speak with the leader of that faction.
