It was the Unyson plugin that caused the error. It finally works now when I have inactivated it.
Okey, so I got the original post from the demo to switch featured image but I can´t change featured image on newly created project pages. The option to change featured image is on the right side but when I set an image and update the page wp removes the featured image again. Help please…
Solved! Sorry for my two tickets today that I finally solved myself. I had to change the settings in WP – Settings – Media.
If I change the portfolio layout to slider the images gets full resolution. But If I change back to default they are low resolution again.
As a side note. If I chose slider my project portfolio slider lightbox has 9 images, but I have only uploaded 3 in the gallery. The slider has 4 (gallery images + featured image), but if I click on them the lightbox has duplicated some images so the number is 9.
I finally got it to work. I had to permanently delete the featured image from the demo to be able to switch. Strange..
It’s called featured image btw, I called it selected image in the first post.