Connection was reset when saving a post

I get this really annoying error which shows up whenever I try to save / publish a post or activate a plugin. The site itself runs fine, and you can login to the admin panel without any problems as well. It’s a fresh installation, which I re-installed twice already, but I can’t get rid of the “Connection was reset” error, which is only triggered when saving / publishing a post or activating a new plugin.

One strange thing I noticed is that when I do view source in the admin panel, is that the code is cut of. This is the last line I see with view source in the admin panel (I already re-uploaded that folder as well, but no changes)

This is how the html ends with view source, clearly there is stuff missing. But all the graphics are in the right place though.

<li id="wp-admin-bar-user-info" class=""><a class="ab-item" tabindex="-1" href="https://mydomain.nl/wp-admin/profile.php

It’s the latest version of WP. I also enabled the debug option in the wp-config, but that also didn’t show anything for me. Error logs on the server, the same thing.

Anyone had this before? Any idea’s what could be causing this? It’s a clean installation without any extra plugins or theme modifications.