I found the problem myself. The $PATH variables on the target server were wrong. For some reason the $PATH variable in /etc/environments had been rewritten to a PLESK PHP version and had an error.
Unfortunately, I get the following error during a Plesk migration. SSH connection works (password and key) and the file is also available. Can you perhaps help me with the problem?
Destination Server: 18.0.28 Debian 8.0 1800200720.10
Target Server: 18.0.32 Ubuntu 18.04 1800201221.13