[Ben Bland]

Maybe a few years too late for your problem, buuut… here’s what I did to solve this same issue, after trying everyone else’s suggestions.

Look at where the playhead is. In my case it was way off somewhere on another part of the timeline, so the composition that I was trying to edit was not visible because it wasn’t active at that particular point in the timeline. With the composition open, I just clicked on the Time Ruler at the top of the Timeline and voila, the composition appeared.

Dumb, maybe, but easy to do.