I think Daniel could be right. Try it without the Motion Blur if you have it on.
Here is another hunch: Do you have 2D layers both above and below 3D layers? Sometimes this not only causes weird things to happen, but also, things may render differently than they appear in the preview. Sometimes this applies to comps within comps also. See this thread:
https://forums.creativecow.net/thread/2/960801
Still another possibility: Are you using the Collapse Transformations option? Sometimes when you have it on / off it can cause unexpected things when you’re dealing with cameras within cameras (or non-camera layers within camera layers), etc.
I’m still learning the nuances of all these myself but often when I have odd glitches things like this are involved and messing with them can help.