I have about 20 scheduled tasks, some run once a day some run every hour or so. There are few that just fail and then work fine when they run the next time.
I've had a look at the Task History for the tasks that run every hour and the Duration is random, it will say it completes in 2 minutes then the next time it runs it can take up to 20 minutes. Most of the tasks are connecting to the same server and there does not seem to be any issues on the server it connects to?
The client build 11.0.11414.0
Microsoft Windows Server 2003 R2
Enterprise x64 Edition
Six-Core AMD Opteron(tm)
2.41 GHz, 63.9 GB of RAM
Any ideas why they would have random runnable times? Is there anything I should be checking out for?
I assume that your server had to different times a different consumption of cpu+ram+network. Beside them your server is an AMD which could struggle on this what meant the server isn't always able to divide the task on all cores and is sometimes using only one core. AFAIK this is a known incompatibility between AMD and QV and using AMD as cpu is not recommended. Maybe you could improve this behavior with some server settings.
The link is quite old and not explicit AMD related but it could be a hint for you for what you should looking for:
One thing I found that helped when I had tasks randomly fail and then work the next time was to change the heap size in regedit. It is recommended to change it from 768 to 2048. Where and how to do this can be found on pg 113 of the latest QlikView server reference manual.