I sincerely hope I'm posting in the right place (I'm quite new here)...

I've been playing through Dragonborn for the first time this week (Xbox 360) and I noticed something odd when I was finally able to pry myself away from Solstheim and return to Skyrim... Once I'd fast traveled back to Skyrim, quite a few locations I'd already discovered (and dungeons I'd cleared) were suddenly blacked out as though I'd never been there and I'm no longer able to fast travel to them. Is there some significance to this I'm missing (i.e. locations lost after visiting Solstheim now have new content) or is it more likely a glitch?

I also apologize if this has already been covered... I skimmed through the first few pages of posts and didn't see anything on the subject.

Thank you in advance!

never came across this myself when playing the dlc but hardly surprised, i had a bug where the cultists didn't show and the main dragonborn quest would not activate had to make a new character

I have never heard of this and it is most certainly a glitch.

I don't know the details of your incident but as long as you complete 'The Greybeards' quest (the quest where you visit them the first time) then you do not need the cultist to start the DB questline. All you have to do is go to Solstheim at lvl 20+ (I think there is a level requirement but I may be wrong) and it triggers. -It will only trigger after you complete 'The Greybeards' quest-

Also, you must complete the entire encounter with the Greybeards, all the way till the end when the next quest, 'Horn of Jurgen Windcaller' (I may have that title wrong), activates.

Like I said, I don't know the details of your incident so if you already knew this and it still did not trigger when you went to Solstheim then I apologize.

TIP: What I do is fast travel back to Ivarstead immediately afterwards and the cultist are there everytime. It can't guarantee it will work for you but it always works for me.