Hi, we know some users are seeing this bug, we are working on fixing it as quickly as possible. You could try some of these options to see if it fixes the issue. If it does, please let us know as it will help us fix the issue permanently:
- Edit the individual clips with the video, make small edits and then export
- Crop or trim the video in your Photos app before importing into the video
- Try removing some clips and then exporting, then adding more clips to that export later.