engine.log
------------------
2017-11-21 10:15:02,536-02 ERROR [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (DefaultQuartzScheduler2) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] EVENT_ID: USER_REMOVE_SNAPSHOT_FINISHED_FAILURE(357), Correlation ID: 70cc2ffa-2414-4a00-9e24-6b6378408a9d, Job ID: ec197072-7c38-42b6-9aef-99635d4ee135, Call Stack: null, Custom ID: null, Custom Event ID: -1, Message: Failed to delete snapshot '<UNKNOWN>' for VM 'proxy03'.
2017-11-21 10:15:02,537-02 ERROR [org.ovirt.engine.core.bll.tasks.CommandCallbacksPoller] (DefaultQuartzScheduler2) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] Failed invoking callback end method 'onFailed' for command 'a84519fe-6b23-4084-84a2-b7964cbcde26' with exception 'null', the callback is marked for end method retries
2017-11-21 10:15:12,551-02 ERROR [org.ovirt.engine.core.bll.snapshots.RemoveSnapshotCommand] (DefaultQuartzScheduler5) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] Ending command 'org.ovirt.engine.core.bll.snapshots.RemoveSnapshotCommand' with failure.
2017-11-21 10:15:12,555-02 INFO [org.ovirt.engine.core.utils.transaction.TransactionSupport] (DefaultQuartzScheduler5) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] transaction rolled back
2017-11-21 10:15:12,567-02 ERROR [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (DefaultQuartzScheduler5) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] EVENT_ID: USER_REMOVE_SNAPSHOT_FINISHED_FAILURE(357), Correlation ID: 70cc2ffa-2414-4a00-9e24-6b6378408a9d, Job ID: ec197072-7c38-42b6-9aef-99635d4ee135, Call Stack: null, Custom ID: null, Custom Event ID: -1, Message: Failed to delete snapshot '<UNKNOWN>' for VM 'proxy03'.
2017-11-21 10:15:12,567-02 ERROR [org.ovirt.engine.core.bll.tasks.CommandCallbacksPoller] (DefaultQuartzScheduler5) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] Failed invoking callback end method 'onFailed' for command 'a84519fe-6b23-4084-84a2-b7964cbcde26' with exception 'null', the callback is marked for end method retries
2017-11-21 10:15:22,582-02 ERROR [org.ovirt.engine.core.bll.snapshots.RemoveSnapshotCommand] (DefaultQuartzScheduler10) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] Ending command 'org.ovirt.engine.core.bll.snapshots.RemoveSnapshotCommand' with failure.
2017-11-21 10:15:22,585-02 INFO [org.ovirt.engine.core.utils.transaction.TransactionSupport] (DefaultQuartzScheduler10) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] transaction rolled back
2017-11-21 10:15:22,599-02 ERROR [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (DefaultQuartzScheduler10) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] EVENT_ID: USER_REMOVE_SNAPSHOT_FINISHED_FAILURE(357), Correlation ID: 70cc2ffa-2414-4a00-9e24-6b6378408a9d, Job ID: ec197072-7c38-42b6-9aef-99635d4ee135, Call Stack: null, Custom ID: null, Custom Event ID: -1, Message: Failed to delete snapshot '<UNKNOWN>' for VM 'proxy03'.
2017-11-21 10:15:22,600-02 ERROR [org.ovirt.engine.core.bll.tasks.CommandCallbacksPoller] (DefaultQuartzScheduler10) [70cc2ffa-2414-4a00-9e24-6b6378408a9d] Failed invoking callback end method 'onFailed' for command 'a84519fe-6b23-4084-84a2-b7964cbcde26' with exception 'null', the callback is marked for end method retries
------------------
I don't have vdsm log. (I don't know why).