Ditto what they said - it’s the wood - BUT
Let me add to your workflow to try and save you on some of these. When your cut is done you should reach in and remove the cut pieces while your base is still held down by whatever you’re using (honeycomb hold down pins being the gold standard).
That way you know automatically if a piece hasn’t cut and you can close the lid and run another cut line in the area that missed.
Now in the case of voids, it may not matter since the glue they use often won’t ever cut, but it gives you a chance!
On pieces you’ve already pulled I find that you can often cut the tiny lines with an xacto blade. It’s worth a shot in any case since otherwise the cut is a total waste.