How to resolve unsecure links of images?

Looking at the page source code, the images are referenced with a http link, but in the sourceset they are a https link. Sometimes both links come correctly as https link, but even creating a new page and adding new images, more often they come as http. How can I resolve that so that new images are created automatically with a https link?

• This topic was modified 5 months, 3 weeks ago by martinneumannat.

The page I need help with: [log in to see the link]