ERR_CERT_AUTHORITY_INVALID on WordPress
Why it happens on WordPress
WordPress sites behind a plugin-managed certificate (Really Simple SSL, host auto-SSL) often serve the leaf certificate only after a migration, dropping the intermediate that proves the CA.
The fix on WordPress
Re-issue the certificate from your host's control panel so the full chain is installed, then clear any caching plugin and CDN cache. Run the SSL check below — it reports the chain exactly as browsers see it.
Is ERR_CERT_AUTHORITY_INVALID happening on your domain?
An external SSL check builds the chain from scratch with no local trust store shortcuts, so it shows a missing intermediate that your own browser may be silently caching around.
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
WordPress has its own failure mode, but ERR_CERT_AUTHORITY_INVALID has a wider set of causes that apply everywhere. The most common one overall is: the server serves only the leaf certificate and omits the intermediate bundle.
All causes and fixes for ERR_CERT_AUTHORITY_INVALID