End user's occasionally are unable to type or enter / manipulate information

Good day,

I have several users that sign into our internal CRM to enter or change information.  Frequently, the user's will encounter a moment where they are unable to add text and change any existing information.  The interface looks absolutely normal but slightly unresponsive.  By this, I mean when the user clicks in a text filed, the mouse cursor does not change to a Insertion point cursor nor is the text window 'activated'.  This goes the same for any drop down boxes.  

The temporary fix we have been doing is clearing out browser cache every time this occurs.  This seems to resolve the issue for a few days the but the issue soon arises again.

Thank you for all your time and assistance,

fallen