I would like to know this as well I am having the same issue.
With the new update of wordpress, i found out that this has nothing to do with BuddyPress or any theme, it is a bug in wordpress itself. The have tried to fix it, but its still not working well, the menu fills the screen and cannot be scrolled or hidden. I recommend hiding all buddypress menus until the bug gets fixed:
/* =Hide BuddyPress sub menu until it works in mobile phones
————————————————————– */
#wpadminbar .quicklinks .menupop ul.ab-sub-secondary {
display: none !important;
}