The file might be corrupted or only partially downloaded. Check the file size; if it is only a few KB, it may just be a header or a failed download.
If you are a developer, run the following command to see the file structure: ffmpeg -i 5fbfa28f9c45cb25769e3_source.mp4 4. Troubleshooting 5fbfa28f9c45cb25769e3_source.mp4
If you found this file in a specific directory or cloud storage, the alphanumeric string is likely a . The file might be corrupted or only partially downloaded