My themes are set up a little diffrent than normal. Im using a theme switcher plugin…so in mobile view, my main child theme actually switches to another mobile child theme. So the css you are referring to does not exist in my mobile child theme.
I know it sounds crazy..but thats how I have it set up.
I replaced the css you provided, but it is still the same. The button menu toggle shows instead of the horizontal second nav bar with links. It showed in the previos version, and once i updated to the newer version..it stopped showing. I did not change any css at that time.