A recent project I had was doing something where I had comp, I'll call it SONG, that contained a lot of precomps that were looped with loopOut()
Inside of each precomp was two layers, let's call them A and B, and each precomp had three frames of A and three frames of B.
Sometimes A or B for one of the precomps would disappear. The layer would still be visible in the precomp, but it wouldn't be visible within SONG, so instead of the nice cartoon wiggle I was going for, I got the precomp blinking on and off.
I was unable to predict when it would happen, and often just had to play around with things randomly until it disappeared and hoped it didn't spring up in one of the other layers. For an example of how weird it was, sometimes I could duplicate a layer having this problem, and suddenly both the original and duplicate didn't have the problem. Then I delete the duplicate and the original goes back to having the problem.
Anyone have any ideas what I should look for if it crops up again?