Hey I was having the same issue! What seemed to work for me was moving my brand icon to the top left (previously had it top center) and shifting primary nav to secondary nav. Problem solved. Not my ideal layout for the header BUT I'd rather have it look a little differently than I anticipated over the most important parts of my menu not appearing at all on mobile. Honestly this is probably a sign of the times that we need to switch to 7.1 if we haven't already...(that'd be me haha)