So at first everything was fine City went from L0 to L1 no problem, performance was okay ( 40FPS ) on high. Then i went exploring the commonwealth for quite a considerable time, built V88 then decided to check on the status of Sanctuary. I tried Fast traveling there got a CTD, no problem i thought it happens sometimes, then tried again it and it managed to load in but as soon as i looked at the City's direction it crashed. Now i tried to walk into the settlement with varying deegres of success. Sometimes i maned to walk in with horrible FPs then crash other times it just crashed on the edge of the cell. (Note:Remote detonatinon of plots solved the FPS issue.) But i lost my progress in that city. I am curious on what could have caused this.