Offering another potential solution to this error.
If you have a frontend application that makes API calls to the backend, make sure you reference the domain name that the certificate has been issued to.
e.g.
https://example.com/api/etc
and not
https://123.4.5.6/api/etc
In my case, I was making API calls to a secure server with a certificate, but using the IP instead of the domain name. This threw a Failed to load resource: net::ERR_INSECURE_RESPONSE
.