I have faced this issue sometimes and just want to share my experience. Just eliminate the cause from the server and SSL certificate because nothing we can't to fix it.
But sometimes, if your computer has a wrong date and time, it can also lead to this error. Or if your antivirus software block SSL connections, Google Chrome also show this message too. I have faced this situation one time.
I found this useful article from Google, it's listed many useful methods to help you resolve or bypass this error. Check it out!
https://usefulpcguide.com/16666/your-connection-is-not-private/