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:
Can you set your reloads so a task runs on completion of another task rather than running at the same time.
One other thought, if your scripts are accessing data from a database, could there be locks that cause the query to be held until a lock is released. Can you use a NOLOCK hint possibly.
As Bill bbt mentioned, QlikView 11.0 is an old version and you should look at the options to upgrade.