LR Classic CC auto upgraded from 8.2.1 to 8.3 ... with that the ability to export videos in 'Original' format fails. (The progress bar shows action, but no files are exported.) It still can export videos in H.264 format (but obviously downgrades resolution from 4K (3840x2160) down to 1080p which is useless to requirement). I tried clearing video cache and disabling metal video acceleration ... neither addressed the issue.
I downgraded back to 8.2.1 and the functionality returned as designed.
I would suggest that the LR Classic CC 8.3 rev has a functional error with exporting video in 'Original' format.
This is on MacOs 10.13.6