<!-- GOOGLE FONTS -->

<link href='http://fonts.googleapis.com/css?family=Arimo:400,700,400italic,700italic&subset=latin,vietnamese' rel='stylesheet'>

<link href='http://fonts.googleapis.com/css?family=Rokkitt:400,700' rel='stylesheet' type='text/css'>

<!-- //GOOGLE FONTS -->

I suspect this following Google font URL generated from your current template, even this contact page also getting the same issue.

https://www.in-mymind.com/en/contact/uncategorised/hast-du-fragen

If you temporary switch this contact menu item template to protostar, it will not hit that issue.

Can you consult with your current template provider regarding this and see how it goes.

Okay, I think i found out where this template render these above Google font URL on the page.

Those code located at this file JoomlaFolder/templates/in-mymind-1/tpls/blocks/head.php

I already help you updated to load https for those 2 Google font URL, can you report this to your current template provider so the next person will not hit this issue anymore in the future.