phpMyAdmin introduced a security improvement in phpMyAdmin version 4.9.4-1. The improvement sets a new session variable named HMAC_secret at login time. The update to phpMyAdmin version 4.9.4-1 occurs automatically when your server is upgraded to cPanel & WHM version 86.
For some users, the upgrade can result in a temporary interface error upon opening phpMyAdmin and attempting to view a table. This happens if the active WHM or cPanel session started before the cPanel & WHM version 86 upgrade. This is a temporary phpMyAdmin error only, meaning your MySQL databases are safe and unaffected.
If you experience this issue, simply log out of your existing WHM or cPanel session and log back in to continue using phpMyAdmin. For additional information on logging into your server or account, see How to Log in to Your Server or Account.