Slovenian characters not showing in Microsoft Edge and Internet Explorer

I’m using Enfold child theme with some customizations and I’m having problems showing slovenian characters, but only in Microsoft Edge and Internet Explorer. In all other browsers the characters are showing OK.
I’m using Josefin Sans as “Heading font”, but IE and Edge for some strange reason always replace special characters (č,š,ž) with some other font (see picture on the link). The rest of characters are showing properly.

I searched the forum and tried different solutions (adding code to functions.php to extend the subset, adding quick CSS corrections etc), but nothing seems to work.
In fact, with adding the “add_filter( ‘avf_google_heading_font’, ‘avia_add_heading_font’)…etc” solution to extend the subset I even completely lost the Josefin font and all the headings were showing as some other generic font – on all browsers!

Any other ideas how to proceed?

Thx in advance.