Best Left Forgotten

Best Left Forgotten is a quest in the Fallout 4 add-on Far Harbor.

Detailed walkthrough
After obtaining Fallout 4 keys the player returns to Kasumi, ending Where You Belong and starting Best Left Forgotten

She will reveal her suspicions about DiMA and give a quest to investigate DiMa's memories, which are stored inside the Nucleus Command Center. Otherwise, the terminal controlling the locked gate to DiMa's memories will remained inaccessible until the player character progresses further in the main quest line.

Once the quest has been obtained the Sole Survivor must travel into the command center in the Nucleus to access DiMA's stored memories. They must bypass radiation, robots, and then solve a series of puzzles to unlock access to the memories.

Through unlocking the memories the Sole Survivor also unlocks the coördinates of several locations on the Island to investigate: DiMA's secret medical facility at the Vim! Pop factory, the location of the Nuclear Launch Key at the Harbor Grand Hotel and the Wind Farm Kill Switch Code.

After uncovering DiMA's secret medical facility at the VIM! Pop Factory the next quest is unlocked: The Way Life Should Be.

Bugs

 * During the first memory the indexers will all cluster against the walls next to the orange memory column instead of returning to the access point, until they are destroyed.
 * There is currently a bug that doesn't let you do the memories. The game will freeze in the loading screen.This can happen on any of the memories, not just one.
 * During the fist memory the small green indexers do not move to the orange memory column despite building a usable path, it may affect PS4 and even PC users as it seems to be very uncommon, this is a game breaking glitch and you cannot proceed further in the quest.
 * There is currently a bug preventing mission completion. On one's first entry to the simulation, it may be impossible to interact with the blocks one must move to make bridges & clear the path for the beam. Exiting the simulation and restarting the console may fix this. Furthermore, turrets are not unlocked for construction when the game informs you to construct them, making it impossible for the player's green indexers to make it to the objective. This renders the quest impossible to complete, even after several reloads and restarts. It may randomly fix on PS4 after returning to an old save. On PS4 returning to the simulation may freeze the game. There is a work around for this bug by using the blocks to imprison the defensive robots before they enter the area, trapping them where they spawn.
 * On certain memories the indexers will not load memory past 80%. This is reported for memory OJ-2NN8 (the second level) and 'the fourth memory' (which should be 0H-3X0P). Then, when one tries to exit the memory simulation, the game can get stuck where one can save the game but can't move around.A possible fix to this: If you are stuck on the 4th memory simulation, leave the keyboard/controller alone until it changes as if you have left the computer. Once it goes to the mode where your character is looking around aimlessly, you can then move the character around.
 * Sometimes the orange data rings will disappear before the indexers are done with downloading the data. Making the quest impossible to complete.
 * On the final memory, placing several Defense Constructs near (or within) the red barrier surrounding the data stream will cause them to fire at the dormant drones, which will then become active. If this persists for long enough, the Defense Constructs will eventually destroy the red barrier itself, bypassing the entire puzzle (note: this takes approximately 15 minutes).

Лучше не вспоминать