I’ve just added a second level menu to my website : was previously About, now is About>Company and About>Partners. Unfortunately, clicking the second level options is just impossible as the menu closes as soon as I hover the mouse on the second level items… It was the only modification I did!
It seems that bootstrap that you are using is overriding the theme main CSS code. To work the menu properly disable the bootstrap CSS otherwise go to Appearance -> Customize/Theme Options -> Design Options Tab -> Custom CSS paste the following CSS code and click on Save & Publish Button:
#access a {
-webkit-box-sizing: content-box;
-moz-box-sizing: content-box;
box-sizing: content-box;
}