In regards to this, the latest status is as follow.

I have found that the NAS being used does not allow us the proper performance we should obtain. When accessing a file on disk or simply by verifying if it exists, was taking a considerable amount of times. For the most used files, the related images used for the lists and forms, I have adjusted the framework to load them all in memory at first. Then, I can manipulate them during the hit without having to go on disk. The performance was a major boost in the right direction. So, this has resolved that part of the issue.

Since then, I was not able to face the long delay period and only time will tell with more testing. However, my assumption so far is that a significant amount of file accesses in the same second for a specific hit, on that particular NAS, might have been a trigger to put it off scope.