Ok here are the exact steps to activate the Miles Eckhart Arlington Gang quest line.
Mission 1: Tracker Training Permit Certification, Pick-up in Crusader, Cost 500 UEC
Mission 2: Bounty Hunter Contractor Evaluation, Pick-up in Crusader, End in Hurston, Payout 4000 UEC
Mission 3: Tracker Beginner's Permit Certification, Pick-up in Hurston, Cost 1000 UEC
Mission 4: Verified Freelancer Bounty Assessment, Pick-up in Crusader, Payout 4000 UEC (this one I don't know, you might can skip)
Mission 5: Wanted: *** (LRT), Pick-up in Hurston, Payout 5000 UEC
Mission 6: Wanted: *** (VLRT), Pick-up in Hurston, Payout 5000 UEC
Mission 7: Wanted: *** (LRT), Pick-up in Hurston, Payout 5000 UEC
After these 3 you get a promotion.
Mission 8: Tracker License Certification, Pick-up in Hurston, End in Crusader, Cost 2500 UEC
Mission 9: Wanted: *** (MRT), Pick-up in Hurston, Payout 7500 UEC
Mission 10: Wanted: *** (MRT), Pick-up in Hurston, Payout 7500 UEC
Mission 11: Wanted: *** (MRT), Pick-up in Hurston, Payout 7500 UEC
Mission 12: Wanted: *** (MRT), Pick-up in Hurston, Payout 7500 UEC
Mission 13: Wanted: *** (MRT), Pick-up in Hurston, Payout 7500 UEC
Mission 14: Pro Tem Group Warrant Contract, Pick-up in Hurston, Payout 26250 UEC, 3 Bounties (Might can skip this)
After these 6 you get a promotion.
And the Journeyman Tracker License Certification is now available to do. But at this time is when the Miles Eckhart Arlington Gang quest line also pops up.
Go into Person-->Appointment
View attachment 20024
The Arlington Gang quest line is made up of 6 missions.
Mission 15: Les Arlington, Pick up from Miles Eckhart, Eclipse
Mission 16: Nicks Cantwell, Pick up in Hurston, Valkyrie? (if I remember right)
Mission 17: Sam Arlington, Pick up in Hurston, Hurricane
Mission 18: Oslo Arlington, Pick up in Hurston, Vanguard Warden
Mission 19: Kass Dent, Pick up in Hurston, Retaliator
Mission 20: Maltrox Arlington, Pick up in Hurston, Hammerhead
Note that after Mission #19 I'm going from memory since it's not possible for me to take down a Hammerhead on my 2nd account.
After completing Mission #20, you will get a request to visit Miles Eckhart again. I assume that you don't need anymore BH rep to continue.
He will give you the below mission.
Mission 21: Group Warrant Issued, Pickup from Miles Eckhart, Payout 17500 UEC, 3 bounties 2 in Hurston 1 in Crusader.
View attachment 20025
Mission 22: Group Warrant Issued, Pickup in Hurston, Payout 26250 UEC, 3 bounties 2 in Hurston 1 in Crusader.
View attachment 20026
Now your done. The Idris Stolen By Arlington Gang should pop up, might have to give it time or hop a server.
I believe that once you kill the Idris, all you have to do is repeat Mission #21 and Mission #22 again for the Idris to respawn. Haven't test it yet incase it's a one per player.
Edit:
Confirmed. Once you blow up the Idris, all that is required is for you to repeat the Group Warrant Issued Missions 2 or 3 times. Pick the good payout ones but not the 87k one as it slows you down with a HH.