SSL Certificate Errors: Why They Happen and How to Fix Them (Without Downtime)

SSL certificate errors are revenue killers: browsers block access, users lose trust, and forms stop converting. The good news is that most SSL issues are operational mistakes (renewal, chain, redirects, mixed content) and can be fixed safely with a disciplined process.

Common SSL errors

• Certificate expired (renewal failed or wasn’t deployed).
• Not trusted (missing chain / intermediate certs).
• Hostname mismatch (wrong certificate for domain or missing SAN).
• Mixed content (HTTPS page loads HTTP assets).

Renewal failures

• ACME challenge failing due to DNS misrouting or blocked HTTP path.
• Wrong virtual host selected in control panel.
• Multiple web servers/proxies and the cert is deployed to the wrong layer.

Missing chain / intermediate certs

Many servers need the full certificate chain (leaf + intermediates). If you only install the leaf certificate, some clients will fail trust validation.

Hostname mismatch

• Cert covers www but not apex (or vice versa).
• Stale redirects send users to a hostname not covered by the cert.
• Old subdomains still referenced by assets or links.

Mixed content warnings

• Hard-coded http:// in CSS/JS or templates.
• External resources (fonts, scripts) loaded over HTTP.
• CMS database content with old URLs.

Redirect chains and canonicalisation

SSL issues often surface when redirects bounce between HTTP/HTTPS and www/non-www. A clean setup uses a single canonical hostname and a single redirect.

• Pick one canonical: usually https://example.com or https://www.example.com
• Redirect everything else to it in one hop
• Set canonical tags to match

Safe change procedure

• Confirm DNS points to the expected server.
• Verify certificate coverage (SANs) includes required hostnames.
• Deploy certificate to the correct layer (proxy/web server).
• Test with browser + command line, then monitor logs.