Shadowbox JS only working on some posts …

Hi, can anyone tell me, why the Shadowbox JS plugin only works on some post, and not all ?

example: For this post – https://jsj.dk/the-white-house/ it does not work

for this https://jsj.dk/en-lang-dag-i-tivoli/ and this https://jsj.dk/vinm%C3%B8ller/ it does work …

I’m confused ..

Thanks for any tips for getting this to work ??