I have two similar CPT´s with the same fields ("kurz" and "teambuilding" ones):
For example hidden link and hidden link
I followed the description how to build Flexslider slideshow for images and it works great at hidden link but it doesn´t show up on hidden link (see section SLIDER – START and SLIDER - END, where it should display). I also created the test part (see TEST – START and TEST - END), where the images and conditional are shown without the Flexslider - it works fine. I can not find, what can be wrong.
Template for teambuilding: hidden link
Template for kurz: hidden link
So the issue with this one is that there is an error in the console on the page. Its complaining about the mobile menu.
What I recommend doing is to create a perfect clone of the working template and then try and see if the slider works there. If it does then you can begin customizing the page for your specific need.
I have made a clone of working template: hidden link, but it still does not show the slider. I also tried to create test section and the images shows correctly without slider. I still can´t find what´s wrong.
It seems that there must've been something wrong with the post that you had created because the reason why it was not working was because of an error on the page.
But I found another strange thing. I have added some new posts of the same CPT type (different from my previous posts in this thread). Every post has more than one image, but the slider shows only the featured one except this post: hidden link
Others show just one image: hidden link , hidden link ,..