This has been happening for a couple of weeks for me.
I've tried different computers.
And different browsers.
I can't find a pattern between the computers.
But on a specific computer, if the match history is broken for a specific browser, then it stays broken.
So for computer X, Chrome is broken - and stays broken.
And for computer Y, Firefox is broken - and stays broken.
And for computer Z, both Chrome and Firefox works.
Clearing history, cookies, everything, then rebooting does not change the behavior.
Also see the following posts complaining about the same thing.
I wish something would be done about it.
http://boards.na.leagueoflegends.com/en/c/bug-report/wbapGYcc-is-match-history-broken-for-anyone-else
http://boards.na.leagueoflegends.com/en/c/bug-report/Wc8FPGcI-match-history-bug
http://boards.na.leagueoflegends.com/en/c/bug-report/Ka7QIM0t-match-history
http://boards.na.leagueoflegends.com/en/c/bug-report/EhW6AEPL-match-history-not-working