Mac - Black screen when loading game / "unable to connect to server..." message

Basically after selecting a champion, and the countdown to play finishing, I get a black screen and a message that starts with "unable to connect to server..." pops up. Previously I would click retry or whatever (but not cancel) and the champion loading screen would appear. In the last few days however all that happens is the pop up message comes back. I cannot get to the loading screen. I have also tried clicking cancel and then reconnect in the client. This does not work and I get the unable to connect message.

Obviously extremely irritating. And now I am being penalised for afk, etc. Does anyone have any advice? FYI using a mac.