Okay, I think I figured out what’s going on. Still not sure what the difference is between “Main” and “Responsive”, but the problem menu was the “WooCommerce” menu. Since I gave up that screwed up cart system many years ago (SendOwl both much better and way cheaper!), I had left the menu unselected. Apparently it can’t be left that way. Once I assigned it a menu, the problem disappeared.
Now for the color problem…