Ridiculously laggy client

I play on NA servers from Europe and the client has been incredibly laggy for me today. Logging in takes ages, accepting invites is not responsive, worst of all is that runes and masteries don't always load. Even when selected they get the loading circle instead of a tick.

In game is completely fine. I ended up having to play mf on a Ryze setup, but it ended up being fine. EUW servers are perfectly normal.

Has anyone else experienced such lag? Is it just specific to EU?