Error: RequestCVPixelBufferForFrame returned: 3 for absolute frame: 8443

The error message is saying that there is something wrong with frame No. 8443. It is most likely a black frame. The solution is to expand your timeline and scroll around in the area of frame 8443 and edit it out. You can use a frame-to-time converter to locate the specific point in time where frame 8443 is located . Here's a link to a converter:

https://www.zapstudio.net/framecalc/

Or, you can simply divide the frame rate of the project into the frame number to get the time point where frame 8443 occurs. So, for a 30 frames per second project divide 30 into 8443. That gives you 214.76 seconds. Divide that by 60 seconds per minute to get the point in time on the timeline in minutes where frame 8443 occurs. In this case, it is the 3.57 minute mark. Scroll around in the general area looking for black frames, white flashes, artifacts or any other signs of corruption. Cut out any that you find and re-export. You might want to work with a duplicate project if you want to preserve your original.

-- Rich