Montserrat is a combined 'variable' / 'static' font
storyline web player does not support variable fonts*
if you install the variable version
- extralight/light/bold/medium/extrabold/... does not work
- only regular and italic is ok
more infos
https://community.articulate.com/discussions/articulate-storyline/font-changing-when-in-preview-published#reply-901400
https://community.articulate.com/discussions/articulate-storyline/problem-with-publish-and-preview-bold-fonts#reply-888008
to fix the problem
- deinstall the 'variable' font version
- install all files from the 'static' folder
* if you take it very precisely, the publish process does not support variable fonts