We have a task scheduled to run at a certain time. Today when it ran there were visualizations missing. The odd thing is that there are different visualizations missing on the two copies(for two different users) that were created and delivered from the same task/report. When we ran the task after sometime, it ran fine(included all the visualizations). what could be the issue?
What logs do I need to check to find, what was wrong with the particular task run?
Andy is correct that the most common cause of this is filters.
Given that you have confirmed you are not using them, check the nprintingsvc.log. Try to compare each stage of the run times between the first run and second run to see if there is an obvious difference that could be caused by an outage or interruption of service.