Error Due to the following Reason:
1. When the Third-party cookies are blocked as shown in the below Image.
2. Then the Inline VF page inside the page layout on Classic UI is not visible.
3. And after a few seconds, the below message is displayed -
"Your browser privacy settings have prevented this page from showing some Visualforce content. To display this content you need to change your browser privacy settings to allow "Third Party" cookies from the domain placementinc2-dev-ed--dragdroptocloud.vf.force.com. Alternatively, if your browser is Internet Explorer, you can add placementinc2-dev-ed--dragdroptocloud.vf.force.com to your trusted sites list on the security options page."
The below the Solution:
1. When the Third-party cookies are allowed as shown in the below image.
2. Then the Inline VF Page inside page layout on Classic UI is visible as shown in the below Screenshot.
