Join Link Not Displaying

I'm having the same issue, I found a way around it by looking through the source code of the page and finding the token for joining, if you want to do it view source on the page and ctrl+f "data-secret" and the long string of letters/numbers following it is the token. Take that and add it at the end of the URL with your league number before it, you can find your league number in the original URL.

http://fantasy.na.lolesports.com/share/join/league/(leaguenumber)/(token)

example: http://fantasy.na.lolesports.com/share/join/league/375750/0puA7eVga6tkC67LysQh