You probably know that the achievement is problematic. So first of all, we'll reset the DLC to get rid of any bugs, either present or potential.

I highly recommend to back up your game data beforehand, as all the progress you've made after the mission Take Control will be erased.

To make a backup, do the following:
1. Navigate to the Steam directory (C:\Program Files (x86)\Steam by default).
2. There, find and open userdata.
3. Open the folder with your ID. Usually, userdata contains only one folder inside, so there shouldn't be a problem.
If there are multiple accounts present on your device, choose the folder with your ID. This guide will be helpful:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2976796532
4. Find and open the 870780 folder.
5. Once inside, open remote.
6. Copy all the files from remote to a new folder, either USB drive or any other directory.

Your saves look like this

This step is vital, so don't skip it.

On the title screen, select Mission Select, then Endgame:

Confirm the overwrite:

The game will start automatically. You'll appear in the director's office, and a few seconds later The Foundation will be started.

Go to the Central Executive and move closer to the elevator. Alan will begin his speech

Wait until he finishes, then go inside. If everything's okay, you'll be notified that the objective of the mission "A Dark Place" has changed. It's important to make sure everything goes like that, especially if you have an older system like mine, otherwise the "Investigations Sector" button may not appear in the elevator.

Use the elevator to descent into the Investigations sector.

Once you're in the Investigations sector, proceed as you'd normally do.
Claim the first control point (Sealed Firebreak/Sector Head Office).

Traverse the Oceanview Hotel, then move to the Abandoned Offices. Claim the control point here.

Proceed and claim the third control point (Operations Corridor). Note that it'll be the last control point you should claim!

Now, teleport to the Sealed Firebreak. We'll start from there and start working with the nine vending machines shown on the map below. Any of them could be possessed, so once you see one, shoot it.


If it's possessed, it'll start levitating and glowing red after being shot. In a few seconds, it will start moving erratically, so consider using the assist mode (one-shot kill) or do your best to keep up with it.
Don't be afraid of losing the machines though, as they'll be reset after you quit the game.
In my case, number 3 was possessed; now it's moving towards the firebreak.

Numbers 7, 8 and 9 are on the second floor of the dark room, which is right after the Operations Corridor control point.

Sometimes there could be two or more possessed machines in the same run, so once you find and destroy one, it's worth a shot to follow the route and shoot them all, including numbers 8 and 9.

To reset the machines, quit to the main menu and load the last save. Follow the route again. If none of the machines is possessed, repeat this step.