Hi guys, I would like to post a potential Solution in regard to this Achievement as this one glitched for me, after doing some research it turns out a few Achievements on the game have glitched for many gamers.
I can't take any credit for the steps below, that goes to Killersquirelz
. I recommend you try this if you do find yourself with a glitched 'Joined the Mile High Club' Achievement. These steps may also work for other glitched storyline Achievements however I can not confirm that.
1. Firsty, disconnect your console from the Internet. Home button < Settings < Network < Network Settings < Go offline.
2. Do a hard reset, I usually leave it around 30 seconds (probably not necessary)
3. Load the game back up and continue with your game.
4. Once ready, navigate to the DedSec App on your phone and then to the replay section. Proceed to replay 'Hack Teh World'.
5. Now, you will see 4 parts which you can navigate with LB & RB. Choose the final part
of this Operation first (where you are jumping between Satellite's and hacking facilities around the globe)
6. Once completed, follow step 4 but this time, choose to play part 1 (you will be driving Ray to a destination)
7. Once done, follow step 4 again but this time replay part 2 (you will be infiltrating the Galilie facility, see the guide above for a nice simple walkthrough of the mission)
8. Final step - once done the above, follow step 1 and go back online. Achievement should pop within about 20 - 30 seconds.
I hope this helps you guys, I can't confirm that this is a solid solution, It worked for me when I was about to give up on the game.
Please do leave feedback whether it had worked or not, the more confirmation of this; will help others in the future.