Mysterious white space on right side of website — tried everything

Question

I run a multilingual Drupal 7 website . White space recently appeared on the right side. I can't find the cause. It shows up on the German home page but not when you switch to English, unless one logs in. It inconsistently appears throughout the website. It shows up in every major browser except Firefox.

I've combed through the css and html , but I'm missing something here. Can someone please take a look?

"overflow-x: hidden" is not really a solution for me — I would like to pinpoint the cause.

Here's a CodePen Link .

Answer 1

It is the following class causing the issue:

element-invisible

It is used on the h2 header here:

Sekundärmenü

To see for yourself, just do a rename on the element and you will see it fixes the issue.