The 403 errors are caused by ModSecurity Rule ID 942440 incorrectly flagging encrypted cookie content as an SQL injection attempt. To fix this, whitelist Rule ID 942440 in your Plesk ModSecurity settings.

Rule ID 942440 is a ModSecurity rule titled "SQL Comment Sequence Detected" ([msg "SQL Comment Sequence Detected"]).

It is designed to detect patterns within requests that resemble SQL comments (like -- or ---), which are often used in SQL injection attacks.