A site, or your site?
As I said:
I saw this randomly at my sites, as well as at other sites
The GDPR does not control what your browser displays, nor does it control whether Adsense displays an ad on a publishers page.
The GDPR no, but Google wants to be compliant. So when I said GDPR-related, I mean, something Adsense is doing to fulfill GDPR (and ePrivacy directive).
As I said above, adsense produces a cookie when it happens, called "test cookie", with the string "Check for consent". So this is related to GDPR / Cookie Law.
The cookie law, says you need to obtain "a" consent, before drooping a cookie. Web sites refined it as "if someone is informed and continues, then this is a form consent", which is generally admitted . Different regulators are also flexible about this, but there is no clear definition of what is "continue", some regulators consider that a "continue" is when you click on the page, to go to a second page, others consider that "scrolling" the page, is acceptable. But in all events, a site is not supposed to drop a cookie, before an action from the user. So, I think that what I am observing is an experimentation from Adsense. Wait for an interaction with the page, before serving ad and the cookie. Otherwise, why would they drop a cookie named "test cookie" with the value "check for consent" ?
And yes, it does sound like the missing ad issue related to Brand Safety.
With due respect, "no". When I visit the home page, of a big EU site, it's the same. And as I said, refreshing "immediately" the page, and ads are showing. It takes half an hour or a whole hour before ads show, because of brand safety, so may be some sites get crawled faster, but not in a matter of seconds. And, if I clear my cache, and return to the exact same home page, of this exact same big site, then again the first hit is not showing ads.
But also, it seems to be randomly.
Adsense knows its in the target of the EU regulators, and being carefully watched. Adsense tried to put the responsibility of any problem to publishers, but it didn't work, regulators said that both the publisher and adsense are liable. So, Adsense has to show its good will, and show that they respecting are closely as possible things.
