Hi Timo,
Thank you for the details!
I managed to find an issue, it is actually a bug with the Safari browser. When live loading elements, Safari is not able to render the images, when the srcset attribute is present. I have found bug reports from years ago about this, but seems like they never bothered to fix it.
Anyways, I had to log-in via FTP and make direct changes to sort of remove that attribute, now it should be okay. I will make sure to have this implemented in the upcoming release, so you don’t have to worry about it anymore.