[ovirt-users] stucked snapshot, locked disk

Hello, we are using ovirt 4.2.8.2-1.el7. One our user probably tried to preview taken snapshot but the task is stucked and never finished. Also disk is locked. Here is engine.log https://pastebin.com/izBJ1BUg I am not sure what went wrong except one java.lang.NullPointerException error... Could it be some bug? Also I would like to unlock disk and clean this task. I can see locked snapshot and disk [root@ovirt dbutils]# ./unlock_entity.sh -q -t snapshot -c Locked snapshots vm_id | snapshot_id --------------------------------------+-------------------------------------- df27ee13-9961-41d5-a4eb-bbb0aadf9086 | 58998020-08cb-4c84-8847-0cb6790724ba [root@ovirt dbutils]# ./unlock_entity.sh -q -t disk -c Locked disks vm_id | disk_id --------------------------------------+-------------------------------------- df27ee13-9961-41d5-a4eb-bbb0aadf9086 | f6405448-baf8-4cc2-8ee7-798ca11cad10 but no runnig tasks [root@ovirt dbutils]# ./taskcleaner.sh -o t but in ovirt-manager I see this stucked task... Preview VM Snapshot predsysprep of VM install_10_64bit_LTSB_UK_ucebny - Started: Feb 12, 2019, 11:28:04 AM Validating - Completed: Feb 12, 2019, 11:28:04 AM Executing - Completed: Feb 12, 2019, 11:28:15 AM Creating Volume - Completed: Feb 12, 2019, 11:28:15 AM Finalizing - Started: Feb 12, 2019, 11:28:15 AM what is best approach to unlock and clean this? Thanks in advance, Cheers, Jiri