Retrieving Data Error[Client][Crash]

I have zero problems in ranked, normals, ARAM, bots, whatever. But whenever I try to play a ranked team game I join the team, queue up, get into champ select and after a few moments everything starts going wrong. I usually make it through the ban phase okay, but as soon as people start selecting champions I stop receiving inaccurate information from the client. It'll show the wrong champs selected, fail to properly swap focus to the players currently picking, no show champions having been selected at all. On the off chance that it finally manages to display that it's my turn to pick, if I attempt to pick a champion it gives me an infinite Retrieving Data: Loading message that doesn't go away.

When the client inevitably dodges me, it shows the other players leaving game, but leaves me stuck staring at the rage-inducing bug I'm trying to deal with. And I can't properly test this bug or try to work around it because Leaverbuster is totally screwing me and my team and preventing me from starting games.