This keeps happening to me:

Running latest Chrome on Mac (High Sierra). Problem occurs once or twice a day, usually goes away with page reload. When it occurs, I can't access the submenu, because as soon as the mouse enters the space between the two menus, the menus disappear.

This will happen if the menu is clicked to try to open the popup/submenu. It's setup to create the popup onHover, and I haven't looked at why a click floats the menu.

7 minutes ago, khawk said:

This will happen if the menu is clicked to try to open the popup/submenu

Hah. Nice catch! I didn't realise I was accidentally clicking.