It happens to more than some customers that the Publisher Distribution Tasks n times longer just to distribute.
Have a look if the MS KB2600217 is installed on your server(s) because There's A Known Bug with .NET Framework 4
It was identified that there is a known bug with .NET Framework 4 that could be causing performance issues:
Reported to SE as Bug #49702 - closed as 3rd party bug:
This issue is caused by a memory leak in Microsoft FileSystemWatcher in .NET Framework 4.
The symptom is that tasks take longer and longer tor run. A restart of the Qlikview Distribution Service will temporary solve the problem. This has to do with the number of something called "Pinned objects". This number is usually in the region 0 to maybe a couple of hundred. At some customers it has been seen growing to millions. The number keeps growing until the Distribution service is restarted. As the number increased, so does the task execution time - until QDS is restarted. This can also be seen as the Distribution service consume a lot of CPU even when no tasks are running.
A restart of the Distribution Service temporary solve the issue
It can be fixed by applying an updated detailed here: