Google AdSense is “temporarily experiencing delays during the coronavirus (COVID-19) pandemic,” which means that Google is unable to review some sites at this time. Google is posting this message in the site review section of the AdSense console for some sites.

Here is a screen shot of this notice from Sunny Ujjawal on Twitter:

I am not sure how widespread this issue is, if it is impacting 100% of publishers who request site reviews or just a certain percentage.

Forum discussion at Twitter.