Thanks for the files - very easy to see.
At first I thought the issue was in the video export the frame time we were supplying to the video element did not match the time for the video, but with 25fps it is so cleanly divisible (0.04 for each frame) that is clearly not the problem!
I found the real issue is that the render of the video may not be complete at the time we take the capture; setting the video’s currentTime can simply take a bit of time. I’ve added a delay for capturing if we find a video on the frame, and that solves the problem (as long as the computer isn’t under considerable load).
Unfortunately I don’t think there any way to work around this issue with the current version. Maybe an iMac Pro could solve it . You’re welcome to join the v4 beta, as this fix will be in the next build.