Same for me. The match history in the client works but on the LoL website it's just a blank page with a border. The client only shows 20 matches. So that doesn't help if you want to look at stats for a champion you haven't played in a while.
This has been a problem on and off. My Chrome extension may fix your issue. Original post.
Some folks are experiencing a 403 issue with AWS, in which case this extension won't fix the issue.