The conditions for having the mobile navigation bar pop up instead of the regular one are better, but the bar is still gone on (some) mobile browsers.
It's not related to the mobile-specific style rules, as it happens when you request the desktop site on mobile browsers as well. I'll try to track down what's going on, though any help with this would be neat, as it's a bit hit 'n miss to run Android browser debugging tools on Blackberry.
Edit: Was caused by new defaults set by both Chrome and Firefox which make it so that they refuse to proceed with any plain http requests if the site was loaded over https. This made it so that jquery was not loaded (and the theme maker wisely decided not to make a fallback for it), which as you all have probably figured out by now, was required to display the burger menu. I never ran into the issue because I was too stubborn to update my bookmark to the https version of the site