ERR_SSL_PROTOCOL_ERROR on WordPress
Why it happens on WordPress
A WordPress site behind a host that terminates TLS separately often ends up with the site URL forced to https:// while the vhost on 443 has no certificate — the redirect loops straight into a failed handshake.
The fix on WordPress
Confirm the certificate is installed at the host level for the exact hostname in Settings → General (including or excluding www — they are different certificates). Disable any 'force SSL' plugin while testing so you can see the raw server response.
Is ERR_SSL_PROTOCOL_ERROR happening on your domain?
The SSL checker reads the live handshake: protocol versions offered, cipher suites, chain completeness and expiry. If it cannot complete the handshake either, the fault is server-side and not your browser.
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_SSL_PROTOCOL_ERROR has a wider set of causes that apply everywhere. The most common one overall is: the server only offers tls 1.0 or tls 1.1, which every current browser has disabled.
All causes and fixes for ERR_SSL_PROTOCOL_ERROR