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Thanks for the feedback.
Generally, CA means certification authority. Since now SharePoint is using https protocol, the website need to be verified the certificate. You said it has been verified by Microsoft, so this should be right.
Whether you have any issues when you visit your SharePoint site? Could you please capture the screenshot of this message and post it here for further troubleshooting?
If you need any help, please feel free to get back to me with the updates.