Its my personal experience that Sanctuary Hills may have a settlement problem. I made a second game after my first finished, with only the original 5 NPC's. A notion which baffled me when other, under-furnished comparatively settlements ended with settler numbers in the low twenties.
After Putting Food, Water, and Power all above 75 with a whopping 300 in defense Using God Mode of course for the sake of testing and a full play-through later, No one ever came to settle in my Sanctuary Hills. In fact, NPC's like the recovering Alcoholic, now Cola-fiend from Diamond City, that I directly sent there, would disappear after the first in game week of being an established shop runner or farmer. This particular problem happened in the original play-through as well.
Keep in mind, the original play-through began and ended in the first week (Beginning, at Hour one of game release) of the games release, and the Test play-through within the next 2-3 weeks after. So patches may or may not have occurred within that time frame that could of affected the test, but in my case, did not.
Additional Unnecessary to ask questions are answered with, Yes, I kept my Defense score 3x's higher than my resources combined.
Yes, I put a Satellite beacon in EVERY settlement I controlled, Including Sanctuary Hills. (Though not immediately on the original Play-through.)
Yes, the first play-through was almost entirely unmodded. (Save for texture replacers.) The following were not.
Yes, I updated whenever possible. GEForce Drivers included.