This warning may occur when the configured "ServerName" from apache does not exactly match the COMMON NAME field from the SSL certificate. Example:
-> Result: apache shows the warning, even though "domain.com" is perfectly covered by the SSL certificate (via it's SAN entry for "domain.com")
... then the warning will be gone, das "ServerName" now exactly matches the domain name in the COMMON NAME field of the SSL certificate.
Conclusion: You may simply ignore this warning as it does not impact the validity of your SSL installation, or you simply swap ServerName and ServerAlias so that the domain is matching the COMMON NAME in your SSL certificate.