Sounds like it loads, and then something (bumblebee) unloads it. You can check dmesg for signs of it being loaded.
Then look at the journal for errors... You'll need to look at messages for the PID that systemd-load-modules ran as. Messages will not show up for the service. 'systemctl status' shows you the pid, and then you can run 'journalctl -b _PID=$pid'