Two Applications on one ServerIP


I have my Apache2 Webserver with one public IP.
Mailcow and a CMS. The DNS Entries are over Cloudflare now. Now If I enable to proxy www. Subdomain and the root Domain with Cloudflare, but not the mail Subdomain, I see the Mailcow page on the www. Subdomain and root Domain.
If I disable Cloudflare, it is all working.
Can anybody explain me, why I got this Problem?
Thank You!

This seems to be the important log line: [Wed Aug 02 07:59:26.781773 2023] [proxy:warn] [pid 2374041] [client] AH01092: no HTTP 0.9 request (with no host lin e) on incoming request and preserve host set forcing hostname to be for uri