I have noticed this several times trying to join someone to help take down a Uber 9 Dragon, or when they want me to see something. Also when you check their profile you can see what Uber they are in, and you used to be able to join through there. When you accept any invite (or the ones I get) they don't teleport me with no error saying why. I wanted to bring this to your attention and I would ever be greatful if someone polished this up.