Nobody can tell you anything without proper system info or other technical details like comp settings and framerates. This happens when framerates don't match.
Don't just fart around with AE and hope you'll be able to get it to work. You won't. Instead, learn the proper way to use AE from the pros:
I have no idea what you are talking about. The only guess I have is that you are ending up with a blank frame when time remapping or mis aligned frames due to the comp frame rate or the footage frame rate not matching up. IOW 23.976 fps footage in a 24 fps comp is going to have some of the frames, including the out point not line up with the frames in the comp which will give you a brief moment in time that does not have any picture. That hole can reveal a layer below or between two clips.
If that didn't solve your problem then please give us the details of your composition including frame rates, the details of the footage that is giving you problems, and your complete workflow that results in the unwanted result. I'd be willing to bet that if it's not a cache problem it's user error and not a bug.
Thank you very much!