After the service start is complete, systemd verifies for the presence of PID file. If the PID file is not found, the following message can be seen in /var/log/messages and also through systemctl status command.
<service>.service: PID file <file path>.pid not readable (yet?) after start: No such file or Directory
Such messages can be ignored, because the service would still be coming up in the background and creating its PID file later.