Service file exists but is not found by systemd

As hinted at by @JdeBP wrong SELinux file labels are the reason for the behavior. The . character in the output of ls indicates that there is a security context set for the file. So be attentive to the . in the ls output!

cd /etc/systemd/system && ls -lhZ some-other-service.service anfragen-3dkonfig-mapper.service prints

-rw-r--r--. 1 root root unconfined_u:object_r:admin_home_t:s0        440 Mar 19 12:08 anfragen-3dkonfig-mapper.service
-rw-r--r--. 1 root root unconfined_u:object_r:systemd_unit_file_t:s0 457 Feb 24 11:42 some-other-service.service

It can be seen that the other service file has the systemd_unit_file_t label, while the broken service doesn't. This can be fixed with restorecon anfragen-3dkonfig-mapper.service. After this the labels look as follows:

-rw-r--r--. 1 root root unconfined_u:object_r:systemd_unit_file_t:s0 440 Mar 19 12:08 anfragen-3dkonfig-mapper.service
-rw-r--r--. 1 root root unconfined_u:object_r:systemd_unit_file_t:s0 457 Feb 24 11:42 some-other-service.service

systemd now behaves as expected.

-rw-r--r--. 

SELinux restrictions are making life complex for you.