[CLIENT] Client disconnects me during champ select in a strange fashion

Basically when I'm in champ select choosing a champion, I will edit my mastery pages. As I'm editing my mastery pages and saving them, it will consistently unsuccessfully save any changes I've made to them, as well as any other changes (summoner spells, champions, runes) after a certain period of time expires. If I make changes before there's less than 20 seconds left, usually I'm fine. But any time after 20 seconds, I'm screwed.

So, if I may, I'm going to do the best I can to describe what this issue looks like. It starts off by being in champion select, clicking 'save' to my masteries, or changing a summoner spell, or editing any kind of gameplay element (changing champion, changing mastery page, changing runes), and the client not responding, specifically once the countdown timer reaches t minus 20-30 seconds. It's not completely frozen, but it won't respond to any input. The timer will actually stand still at the frozen point. It will also not put me in the game once the timer expires. How do I know that the timer expires when it is frozen? I know because it will then show me that people are 'leaving the room', which is obviously the other players successfully being loaded into the game. Then, I will close the client and try to restart it. The first click on the League executable file gets me no response. The second click gets me a small black screen pop up at the top left of my screen. I will not be able to close this screen, nor will it load into anything. I will then have to log off and then log back in (or start my computer). I will then be able to open the executable file successfully, and I will be able to reconnect to the game before the minions spawn.

This has happened multiple times, and it has left me being put in games with the wrong masteries. It is not fun when I have to face off against a Zed as Warlord's Bloodlust Vel'koz. Please fix this client issue. It is ruining my experience with the game. I should be able to edit my masteries in champion select without issue, as is intended, seeing as champion select gives me the option to do so. Thank you for your time.