Unable to execute pre-configured connectors

I'm unable to execute pre-configured connectors from an alert and from the `/_execute` API. When I try invoking the execute API, I get the following error message:
```
{
    "statusCode": 404,
    "error": "Not Found",
    "message": "Saved object [action/foo] not found"
}
```

The same is logged to the console when using an alert.