I have this problem in general as well, even when practicing though I don't think it ever affected me as greatly as you. All the time doing LR sections, I knew I was slowing myself down because I would be slightly bored so I would read the first sentence and into the second and realize I wasn't actually paying attention or comprehending, and so I'd have to back and re-read it. On the LSAT, contrary to this, after bombing the last game, I was so pissed off and thought the whole thing didn't matter anymore, that I had like crazy focus and wasn't doing that (but I was also speeding through the questions, so I"m sure I made some mistakes). The only thing I can do about it is be aware and try to engage. When it happens, I just try to actively fight it and think about the words I'm reading and what they mean. I know that's probably not that helpful but for me, it's something I just try and force myself to do. It never got the point though where I wasn't finishing sections. It would just slow me down. If I wasn't like that, I could probably complete LR with about 5 minutes to spare, but meh.