Why does MatLab 2017 slow down?

I have MatLab 2017b on Windows 10 with an i7 Intel processor. After restarting the computer and loading Matlab, the MatLab bechmark 'bench' function runs with performance 2nd from top for speed. This performance is repeated for a minute or so until the speed suddenly drops by a factor of about 4 to second from bottom. On re-starting MatLab thereafter, the application loads more slowly and the speed doesn't improve. I have disabled my virus software (Kaspersky), disconnected from the internet, disconnected all USB devices and closed down all the applications I can see. The task manager indicates only MatLab with any significant activity. I am at a loss as to the cause of the problem. Any ideas are welcome.

[Darío Pérez]

Similar problem here still unresolved. Please refer to my comment in: Why my Matlab 2017a is so slow for even simple commands?