How to break "The raod to salthamn" quest (PS4 Co-op bug) (With Fix)

This bug will break “The Road To Salthamn” Quest making it impossible for the Host to progress past this point.

How to reproduce this bug (PS4, needs testing on PC and Xbox)
WARNING!! This will break Player 2’s / (The Host) Game and the only fix so far is to delete the savegame and start again

Player 1 needs to have completed “The Road To Salthamn” quest.
Player 2 must not have acquired “The Road To Salthamn” quest or been to the salthamn bomb shelter safehouse yet.
Player 1 joins Player 2’s game before Player 2 gets “The Road to Salthamn” quest
Player 1 then “Fast Travels” to the “Salthamn Bunker” and turns on the power unlocking the safehouse in player 2’s game before the quest is acquired.
Player 2’s game is now Broken, if player 2 now get’s the “Road To Salthamn” quest they will never be able to “Locate and explore the bomb shelter”, it will never complete in the quest objectives list.

The only solution to fix this bug is to delete the savegame data for Generation Zero and start a new game.
Since quest progression is shared between all player created characters if you break this quest the game is literally broken until you delete the savegame and start again.