Starting a service fails with "New main PID does not belong to service, and PID file is not owned by root. Refusing"

Issue

• Since the upgrade to RHEL 7.7, a service with property Type=forking and property PIDFile defined doesn't start and its status shows the following error messages:

  <timestamp> <hostname> myservice[<PID>]: Starting myservice
  <timestamp> <hostname> myservice[<PID>]: myservice started.
  <timestamp> <hostname> systemd[1]: New main PID <PID> does not belong to service, and PID file is not owned by root. Refusing.
  <timestamp> <hostname> systemd[1]: New main PID <PID> does not belong to service, and PID file is not owned by root. Refusing.
  <timestamp> <hostname> systemd[1]: Failed to start myservice.
  <timestamp> <hostname> systemd[1]: Unit myservice.service entered failed state.
  <timestamp> <hostname> systemd[1]: myservice.service failed.