I think the lock_time in the file xtrabackup_info is wrong. According to the output of xtrabackup the lock was issued at 21:30:04 and released at 21:30:12.
170815 21:30:04 Executing FLUSH NO_WRITE_TO_BINLOG TABLES…
170815 21:30:04 Executing FLUSH TABLES WITH READ LOCK…
170815 21:30:04 Starting to backup non-InnoDB tables and files
170815 21:30:12 Executing UNLOCK TABLES
170815 21:30:12 All tables unlocked
lock_time = 0
this does not match?!
What is the correct lock time?