Sub item menu disappears when I hover over it

Hello, recently I noticed that when I hover over a sub menu item, it disappears and can't be clicked. This seems to be a recent issue but I can't seem to solve it. The first item in the sub menu is clickable, but as soon as I move the mouse down to the next sub item, it switches to the next main menu item in the drop down. I'm not sure how to remedy this? Thanks!