ERR_CERT_COMMON_NAME_INVALID on AWS S3
Why it happens on AWS S3
An S3 static site served over the bucket's default HTTPS endpoint presents a certificate for *.s3.amazonaws.com, which never matches a custom domain.
The fix on AWS S3
Put CloudFront in front of the bucket and attach an ACM certificate for the custom domain in us-east-1. S3 alone cannot serve HTTPS on a custom domain.
Is ERR_CERT_COMMON_NAME_INVALID happening on your domain?
The SSL check reports which names the served certificate actually covers, which is the whole answer to this error in one line.
Free, no signup. Runs from outside your network, which is the only way to tell a server fault from a local one.
If that didn't fix it
AWS S3 has its own failure mode, but ERR_CERT_COMMON_NAME_INVALID has a wider set of causes that apply everywhere. The most common one overall is: the certificate covers the apex domain but not the www hostname, or the reverse.
All causes and fixes for ERR_CERT_COMMON_NAME_INVALID