Frame suddenly dissapears

So I uploaded couple of layers with previous drawn animation into AE in order to apply the watercolor effect on them. Everything seemd to look fine until I pressed play to see the preview. Some of the layers keep dissapearing for the duration of the 1st frame. The dots all over the screen appear instead.

Here you can see that everything is fine, all layers appear. But when I swipe the timeline marker to 01 frame this appears:

Is there any way I can fix that? As you can see, only some of the layers dissapear. I redrawn them (animation made in Toon Boom Harmony)  but the issue remains.

Thanks for any help.