Hi Olaf,
I found something that might interest you (which you most probably know already) and the community.
In Chrome, there's a setting under 'Privacy and Security' > 'Cookies and other site data' > 'Send a "Do Not Track" request with your browsing traffic'

Originally this was turned ON in my Google Chrome browser. I think Google sets this as default (not sure). When this was turned ON, then I couldn't see the creative in the website. After turning it OFF as seen in the screenshot above, then the creative is appearing now in the browser.

Note that in our CI360 Setting that "Honor the Do Not Track (DNT) setting if it is enabled" is selected. Maybe this is causing the non-delivery of the content. Please do correct me if I'm wrong.

To test my theory:
I changed the setting in CI 360 to ignore the DNT

I turned ON the DNT in Google Chrome setting:

I'm now able to see the content/creative in the Chrome browser even if DNT is ON.

More details about DNT:

Regards,
JC