As a seller, you need to follow Amazon's listing title guidelines when creating a listing using the Listing Builder.
These can be found here.
Now, when creating a title, you might see an error message indicating that your current title is not within Amazon's new guidelines. When that happens, you will see the error message. You can learn more about what is causing the issue by clicking on the dropdown button on the right side:
Once you expand the view, the Listing Builder will explain what causes the listing not to match Amazon's new guidelines:
In our example, it was the usage of special characters that were not part of the brand name and the usage of the same keyword more than twice.