Magento 2 - Fotorama Gallery Nav shaft is missing on product page

Question

If you add multiple images to a product then they are showing below the base image in small boxes, see screenshot below (bottom corner - left):

This box is missing. First I thought it is because some change in my theme, so I temporarily changed to luma theme, but the images are still missing, so my custom theme is not the cause.

Is there a setting somewhere which is not set correctly?

I already tried:

grunt clean
php bin/magento catalog:image:resize
php bin/magento indexer:reindex
php bin/magento cache:flush

I am using Magento 2.4.2 Enterprise running in Developer Mode, hosted on a Linux Server (Rackspeed).

Answer 1

I figured it out. A third party extension I have wrote was causing it.

I had overwritten getOptionsJson() and getFSOptionsJson() of \Magento\Catalog\Block\Product\View\GalleryOptions