Thanks for the tip with the Health check tool. This is a really great tool and I found the Problem.
Since I updated on WordPress 5.0.3, the Plugin “WP Cerber Security, Antispam & Malware Scan” causes the Problem. Funny that it is only on the Privacy notice page. But this can be because with WordPress 5.0.3 the Privacy notice is not a normal page but is a Special page for WP.
THanks for your help