heading font not rendered properly

You are using the Montserrat Font from the drop downlist of Enfold Typos?

Are you familiar with inspecting your page with a browser dev tools? Then you can check if this Montserrat font has all those font-weights you like to use.
Or do you have uploaded your own Montserrat font by self hosting it? What kind of Montserrat did you upload then – the static files or the varialble Font?

I would generally recommend hosting the fonts yourself. And even turning off Enfold support for Google Fonts.
It’s more flexible because you can choose the font styles you specifically need, and this is probably the only correct way to be GDPR compliant.
To hamper Google Fonts Support on Enfold – put this to your child-theme functions.php:

function my_output_google_webfonts_script( $activate ){
  return false;
}
add_filter( 'avf_output_google_webfonts_script', 'my_output_google_webfonts_script', 10, 1 );

For selfhosted Fonts – use the Enfold Font Manager – with its upload.
You upload zip files to that font-manager f.e.:

my recommendation is to use definitly woff2 fonts – but maybe as fallback the ttf Variants.
On zipping the Folder (Montserrat) – pay attention if you do that on Mac OSX. Because there are hidden files in there. You had to avoid that.