Displayed does not always mean eligible
A normal reward is issued only when the surf event passes the platform's verification path. Common reasons for no credit include an incomplete timer, failed CAPTCHA, duplicate/uniqueness rejection, lost session state or another traffic-quality rule.
Sponsored Surf Queue Fallback Ads are also intentionally non-reward views, even though a website is displayed in the Surf window.
If normal eligible sites repeatedly fail to credit, note the approximate time and campaign name/ID and send that information to support.