OK, so I have a project I've been working on and it's having a strange issue.
I have some green screen footage composited on a Photoshop image of a piece of glass.
It looks like this.
Here is the 'precomp' for this layer.
And here is the layer in the main comp.
What's happening is that I'll end up with frames that have the glass layer 'behind' the green screen layer for a frame or two, then it 'pops' back to normal. This happens randomly throughout my render.
This is what it's supposed to look like:
Notice the edge of the glass is 'on top' of the talent in the 'good' shot. Also, his suit coat is 'on top' of the glass instead of 'behind' it.
It does show up in the comp on occasion in the RAM preview, but sometimes I can 'page down' through the frames where it's shows up in my render and it's not showing.
Since you're in 3D space, try making sure your z-depth of your layers is literally stacked like you want it (0.01, 0.02...), not just all at 0.00. I get that sometimes in 3D when my layer stack can't (because of compositing needs) be the same as my z-depth order.