Without doing any further investigation: does the type of service you're setting in your user file match the way you're starting up the daemon? For a "normal" service, you need to start the service as "normal" and have it run without forking / exiting (as systemd handles daemonization).
If you start a "normal" service using a command that double-forks and immediately exits (like a `--daemon` flag), systemd will see that the process has exited to mean that the service has finished, and will terminate any of its child processes (as you want runaway dependencies culled when a service crashes). This sounds like the behavior you describe.
If you start a "normal" service using a command that double-forks and immediately exits (like a `--daemon` flag), systemd will see that the process has exited to mean that the service has finished, and will terminate any of its child processes (as you want runaway dependencies culled when a service crashes). This sounds like the behavior you describe.