I don't know why this is, but I am never able to join any of my friends' parties without being specifically invited with the sole exception of one person. It always says "oops" that all friends but him are not join-able even though mutual friends can join without any issues. I am vanguard and can make my own groups of everything I've been unable to join.

If this has been reported before, I can't find it. I have no idea what further information to provide, either, but it's been like this for weeks.