Yes that could be it because your site is having the Mixed Content issue.
If your site has already an SSL certificate your site should not be accessible via non-secure protocol
HTTP anymore, it should redirect to
The site is not loading the font-file because it is being requested from
HTTP which is being blocked. I think this happened because at the time you uploaded/set the font-files the site URL is still in
Now that you have your site URL set to HTTPS please re-set your custom font in the font manager.
Another thing is you can use this plugin to force your site to be accessed via HTTPS.
Let us know how it goes,