Good morning Poriadin and welcome to the NS Community.

I'm sorry to read you're having issues with this. We are aware that the option to download a declaration form of travel history is not working properly and are working on a fix.

What seemed to help for myself is to navigate to a different page in the Mijn NS account after clicking on the ‘Download’ button. For some reason, the download happens a lot faster then. Perhaps this works for you as well.