With Pearl 1.9.1 onwards, drop down menu (or slide out menu in mobile/table) mode does not work sometimes

Hi 

I noticed the with Pearl 1.9.1 onwards, I start to have occasions that after a page is loaded fully, the drop down menu does not appear when I mouse over the menu item. The main menu items are still clickable. When that happens in mobile responsive mode, the menu also does not slide out when clicking on the menu icon.

It is infrequent in 1.9.1 but with 1.9.4 and 1.9.5, it is happening so often that my site is not very usable at all. 

Has anyone encountered this before?

Regards
Donnie