Same problem here. My only "solution" (i.e., non-solution) was to export everything I could and rebuild the project in Logic Pro X...
I'm curious; you say "light" sessions, in terms of track count, but is your score relatively long, by any chance? I seem to start experiencing this as I get further into long tracks (i.e., > 15 minutes, or so). I haven't specifically noticed it in shorter tracks.