Why I don't play LoL
This is not the only reason, but it is a strong one, this happens 90% of the times, no matter if a vs. AI, custom, pvp, or even ... the tutorial!
Should be noted that this happens even with P2P of LoL off and all other network services/apps off. Also, the game usually runs at 40+ fps with everything on max, when recording I was using vsync at 25fps.
I fast forwarded most of the video, but head over to minute 2:00 to see what happens.
During the recording of this video I noticed something that might give a clue for the problem. The issue (lag spike, disconnection, or w/e) happened EXACTLY when the recording application created a new span file for the video, so maybe a file caching system that the game uses? This issue only happens with LoL, all the other games, services or network applications work flawlessly and without hiccups.
Sorry for the bad quality of the video, but I don't like to wait 2 hours to upload the video (and if this takes 6GB (60MB after reencoding for upload) the full res video would eat the entire hardrive space)
So any clue of why this happens? Remember, 90% of the times, sometimes it doesn't disconnect but starts having some horrible lag spikes!
Update: I changed ISP. Though the issue was only solved after several updates by Riot. I think the issue remains, but to a much smaller extent, related with hardrive use during gameplay (for caching reasons perhaps?). Right now, it is very rare to get issues with it. The PC (an ancient laptop by nowadays standards) I use is still the same (minus a few bits and pieces that fell off).