Ok, first of all: great support by Hristian and Mark (from the Unbounce support).
I digged into this, and the problem generated from how I had integrated our cookie consent manager. I had the code twice (once as external script, and once as inline code). This apparently blocks loading stuff from CloudFront, where the images are hosted (or it blocks internal Unbounce scripts from copying the right URI into the image src).
The solution was to throw out the external script.
The path to the solution (as I’ve learned from Hristian and Mark):
- create a new blank page under the unbouncepages.com domain
-> so you won’t inherit any domain wide scripts
- move the page variant, after duplicating it (if it is the only one it will be copied) with destination "new page under unbouncepages.com)
- add every global script you have manually to the page, and test it one by one