Found a thread on this from 2018, but my issue seems to be different. I just thought this was a base quest I had never triggered before. I found a journal on a raider that referenced Edwins cabin, but the description and such definitely made me think of that maze down at the parking garage by Fallon's. That's also where the quest marker showed when I activated this quest, with the stage 'Confront Magnum'. Unfortunately I made it to the top of the garage and nothing there. Just a quest marker. Note, there were no previous stages to this quest which from the other thread I get the impression it should have been given to me by a settler, directed to Edwins cabin first, then from there to the Garage. I just found a journal and it never gave me anything else. Not sure if this is broken beyond repair or if it will start working when I find Edwins Cabin.