Mission chain name is Gathering Storm, just after you encounter Fabius Bile and "defeat" him, the next Mission is that Dark Eldar are (again) raiding your ship, and you need to speak with Thor so that the two of you go and clear the mess.
THE PROBLEM is that you CAN'T speak with Cassius Thor as he just brings the PVP window as you click on him. He should interact with you to begin the Mission but it doesn't happen, just regular PVP search window. Please fix that cause it's FRUSTRATING, the story is amazing and it just started to bild up!