target module not available on remote node

I have a service `calculator` and the `investigator` running through the `libcluster`.

but when I register my service, sometimes something strange happens.

for example:

When I start the `calculator` service it returns me the following message.

```
[warn] [swarm on calculator@127.0.0.1] [tracker: start_pid_remotely] "a475b420-e5f8-4528-9b72-766b7e75d177" could not be started on investigator@127.0.0.1: target module not available on remote node, retrying operation after 1000ms ..
```

and in the `investigator` service I get the following return

```
[warn] [swarm on investigator@127.0.0.1] [tracker: do_track] ** (UndefinedFunctionError) function Calculator.Supervisor.register / 1 is undefined (module Calculator.Supervisor is not available)
    Calculator.Supervisor.register ("a475b420-e5f8-4528-9b72-766b7e75d177")
    (swarm) lib / swarm / tracker / tracker.ex: 1082: Swarm.Tracker.do_track / 2
    (stdlib) gen_statem.erl: 1660:: gen_statem.call_state_function / 5
    (stdlib) gen_statem.erl: 1023:: gen_statem.loop_event_state_function / 6
    (stdlib) proc_lib.erl: 249:: proc_lib.init_p_do_apply / 3
```

but if I try to start it sometimes it works without problems.

can anybody help me?