Board Thread:Love Live! School Idol Festival Lounge/@comment-28606241-20170116184526/@comment-11148831-20170117123717

I'm no iOS user but from what I know, if you had Game Center, then there should be no problems in reinstalling since Game Center backups your game data, iirc. However, if you don't have backups or transfer passcode... well, you know what happens after reinstalling.

Though, SIF JP's downloads have been really annoying recently, ever since the big update. It developed a habit of getting stuck at one point and crashing over and over, even when having full connectivity to the internet. I don't know if this is the case with yours too, but I'd first suggest to be a little bit more patient with it and try downloading again before reinstalling.