421 Misdirected Request on websites

Upon further investigation and discussion with cpanel's support it appears to be that the issue is specifically with the most recent Apache update, regardless of control panel. Specifically if the site is behind a proxy or WAF (cloudflare, sucuri, nginx, etc,.).

cPanel is working on a solution and hope to have it available for update soon.

We have found a temporary fix while we wait for cPanel to implement a permanent fix. Downgrading the EA apache and nginx packages has shown to resolve the 421 errors so our admins are applying this fix to affected servers.

Apache was upgraded to version 2.4.64 to address several CVEs. However, this updated version has been found to cause 421 errors when used in conjunction with EA-Nginx.

The cPanel team has advised that downgrading to Apache 2.4.63 serves as a temporary workaround for the issue.
We are liaising with the cPanel team, who have opened an internal case for their development team to investigate further.

Plesk team is preparing a custom fix for Plesk Obsidian 18.0.70 and 18.0.71.
Workaround for Plesk:
https://support.plesk.com/hc/en-us/articles/33500191748887-Websites-hosted-in-Plesk-are-not-accessible-after-a-recent-Apache-update-421-Misdirected-Request

We will update the status page as soon as more information becomes available.