As I said, if you want to restore on a server that uses the same S3 bucket, make sure to have S3 configured in app.yml and create a backup without uploads (discourse backup --sql_only). Upload URLs won’t be rewritten when the backup doesn’t contain uploads.
If you wish to restore on a server that uses a different S3 bucket, or no S3 config at all, use a full backup with uploads. Upload URLs will be rewritten during restore.
Are you 100% sure that you configured the OVH S3 via environment in app.yml on both servers and used a backup without uploads (.sql.gz file extension)?