I find that if the backup is made on a course (without "Include files" option ) and there is a missing remote file (s3  aws) in the course, the restore will be broken and throw the error at:

line 1082 of /backup/util/dbops/restore_dbops.class.php: call to file_storage->create_file_from_url()

Probably error caused by:

https://tracker.moodle.org/browse/MDL-35773