Apache2 proxy_fcgi:error AH01071: Got error ‘Primary script unkown’

  apache2, linux, php, ubuntu

I recive a lot of Errors in my Apache2 Error Logs that says:

[Thu Dec 02 08:07:33.164090 2021] [proxy_fcgi:error] [pid 9590:tid 140652906006272] [client XX.XX.XX.XX] AH01071: Got error 'Primary script unknown

The System is:

Ubuntu 20.04

Apache 2.4.41

PHP 8.0.13

Any idea what it caused and how to solve this?

Source: Ask PHP