Thanks junior466, this was driving me nuts! I don't understand why WordPress isn't including a changelog. A simple change for them could mean hours of searching for us.
It's also worth mentioning that some custom CSS on child themes could be messing with the display as well. Look for any mention of 'h3.menu-toggle' and replace it with 'button.menu-toggle' Or simply leave it as '.menu-toggle' as you don't need to over-qualify the selector anyway.
If WordPress allowed it, I'd be giving you some major rep-points right now, junior466. I can't believe I missed that. You're my hero.