[CLIENT] Waiting indefinitely at pre-game Loading Screen; One user shown as 'Not Connected'

One time I started a game in Ranked Mode, and went through the picks, bans, etc. without a problem. But when I got to the pre-game Loading Screen (where you see the opposing team's champ masteries, summoner spells, etc.), well I was stuck there. A single, lone user (on my team) was shown as being 'Not Connected', while everyone else was shown as having the game loaded 100% (including me).

After about 3 mins of waiting I checked my internet connection (just in case) by alt-tabbing out and Googling something random; turns out my internet was working fine. I sighed, thinking I would be playing yet another 4v5 match.

I checked my connection periodically, and each time there were no problems with my internet. After about 25 mins of waiting I decided to restart LOL entirely.

Unfortunately for me when I logged on again the League Client was saying something along the lines of 'You have disconnected a game in progress. Please reconnect'. (You know, with the orange box). So I did so.

To my horror I joined a match that had been going on for a half an hour; the other team had pretty much won already, as my team was playing a 4v5 match. I tried explaining what happened after the game, but no doubt I was reported for being AFK anyway, which actually wasn't the case at all.

All that time I was waiting (or so I thought) for that one person to log on again! But instead I was that person!

This happened right after patch 6.6, and I don't know if this is an isolated problem or what, but I sure hope it is resolved. I never AFK in Ranked Matches and I can attest from experience that 4v5's are really horrendous to have to endure and a complete waste of time.

Has anybody else been unlucky enough to experience this problem? If so, what causes it?