Sorry, but why on this page but also on others, the h2 title comes out in the code for both desktop and mobile mode?
If I select a band with "show only on desktop" the html why does it show the same band dedicated to mobile?
That is how Responsive Visibility works. It hides the sections on certain resolutions, but the code for it is still visible in the website's source.
If it is not what you are referring to, please send me a link to your website to take a closer look at it.
Ok but how can we fix this? So is this normal or is it a bug?
This is normal behavior, there is no option to remove it completely using the BeTheme.
To direct you with solution, you have to create the JS script which will remove the not necessery content from DOM on the browser load.
We do not help with this kind of customizations, we only help with little CSS tweaks, help with theme bugs or understanding how the theme works.