Web browser Brave has a feature called 'Shields' which is designed to protect the user's privacy by "blocking most ads and the trackers that come with them".
Most of the time, Shields works fine - but occasionally it can block useful website content (in particular third party / embedded content). When this happens, it is easily fixed by putting 'Shields Down' for the site in question. With Shields Down:
"Protections are 'off' or 'inactive' and the page web page you’re viewing will display and allow all content the site requests to render."
One of the websites inadvertently affected by Brave Shields is Google Ad Manager (formerly Doubleclick for Publishers), though it may take you a little while to notice the problem. Google Ad Manager is certainly usable with Shields Up, but image creatives are not displayed at all. That is, you can't see them in an order, in an individual line item, or within the creative library (accessed through Delivery > Creatives).
This is likely to be because because the creatives are hosted on a different domain - https://tpc.googlesyndication.com/. And I suppose they are ads (or at least become ads when they are served on other sites).
For example, here is what the creative library looks like with Shields Down:
And here is what it looks like with Shields Up:
And it isn't just image creatives - other creatives types are blocked as well. For example, with Shields Up, it is not possible to preview a custom creative. This applies to previewing both in-page and in a new window, and affects creative hosted by DoubleClick Campaign Manager as well as third parties.
I would show you an example of that too, but a screengrab of a single missing creative is the ad ops equivalent of a performance of John Cage's 4'33".