It would help the smart people (I'm not one of them) if they knew what system you're on, and if loading an old save allowed you to go past that point in the game, or if you still get stuck there.
If it were me, I might try using fast travel to go to Goodneighbor and continue the quest there, it's the next step anyway; you'll find him waiting to meet you there. Be sure to save just before meeting Mel for the first time, in case this doesn't work.
My default suggestion for these situations is "log out, shut down & restart". That may clear up whatever is troubling your game.
If that doesn't work, try the solution shown here: -->
Try a fresh install?
Delete your game, reinstall, redownload the patch? Sometimes it works.
I don't have this problem. But I feel your pain.
I was all happy playing on my XB1. After learning I could move more settlers to Sanctuary by wearing charm clothes and drinking, chemming up. I went to settlements with 24+ settlers and was moving them to Sanctuary and Castle (both need to have the 32 I now Know they can have). I then started adding a bar to my Sanctuary. Tried to use the rug collision fix to build my bar into a store. The rugs still stacked but the bar wouldn't go with it, no matter where I moved it, even on level ground. Then I just tried to build a store around the bar merchant thing. And it wouldn't stay on the wooden floor. It would sink through and use the pavement. I tried putting it in my workshop area I built. Which is more than tall enough. It had a very tough time leveling. So I saved and tried to restart the game.
It went though it's intro song, then showed my character. I press continue. It goes through the motions then boots me back to the intro song and rinses and repeats. I excited the game, rebooted my console. Oddly when I hit the Xbox button and menu where it usually shows the quit option, when it is acting silly, the quit option isn't there anymore. Either way, now I can't play. So it's forum time .
So it appears the patch is causing some issues. Hopefully Bethesda is on this immediately.