Error mapping custom domain on Appengine

Question

I'm trying to map a custom domain in a Google Appengine project. Following the instructions listed in the Settings > Custom Domain section of the Google Cloud Platform Appengine Console, I'm able to map a subdomain www to my domain, but the mapping fails for the naked domain.

The error thrown up is: "There is an operation pending for this application. Please wait and try again."

I had earlier set up naked domain redirection in G-suite, but the G-suite account was deleted later. However, this error persists.

Has anyone else faced a similar problem?