QlikView 12.00 QlikView 12.10 QlikView 12.20 (November 2017) and up
To troubleshoot this issue you will need to first check the QlikView Distribution Server logs and particularly the log called root.txt
Looking into this log at the time the task was supposed to be triggered you may find an event similar to:
0171113T072731.006+0100 Information DistributeTask[69a4c453-d6cf-4468-b72d-7161c965cc10] ("TASK NAME"): TryQueue successful. Triggered by 'TaskCompletedTrigger'. Id:a0bb81c1-a493-4fcf-b884-93dbb54e6850. ExecID:c2e91617-8feb-4d5a-92b7-67a3b63e98c0 20171113T072731.068+0100 Information TriggerState: Change State to Ignored. Task="TASK NAME", ExecId=c2e91617-8feb-4d5a-92b7-67a3b63e98c0. Trigger TaskCompletedTrigger ignored. No QlikView Engine was available after waiting for 45 minutes. The first event mention that the task is queued and the second indicates a failure for this task with the following information No QlikView Engine was available after waiting for 45 minutes.
Looking at the time those event have been triggered at the same time meaning that the QlikView Distribution Service has never waited 45 minutes to get a QlikView Engine available.
Increase in disk requirement for QlikView 12.10 and above
QlikView Server 12.10, 12.20, 12.30 and above, are all more write-intensive on disk. If disk write queues are too long, the result can be a previous task execution not having been correctly updated. This will lead to a timeout the next time this task is run.
! Information provided on this defect is given as is at the time of documenting. For up to date information, please review the most recent Release Notes, or contact support at support.qlik.com with the ID QV-14003 for reference.
If not related to bug above, there might be several causes for this behavior and some are listed below: