Hello Ciarán,
On the website Rijtempo: page FAQ we have put in two modules on header-1 position. We've added the classes differently (as described on https://www.joomla51.com/tutorials/item/hide-a-joomla-module-on-mobile-devices) to show/hide one of both modules on desktop + tablet and the other on mobile. But the classes doesn't seem to work. What are we doing wrong? Thanks!