## Bug description

When going to instance status > internal metrics and refreshing the dashboard, the loading fails

https://user-images.githubusercontent.com/148820/120655500-693c7480-c48b-11eb-8c75-6afd4c967506.mp4

## Expected behavior

It reloads successfully

## How to reproduce

See above

## Environment

- [x] PostHog Cloud
- [x] self-hosted PostHog, version/commit: latest

## Additional context

Seems the cause is that "refresh" requests data from `/api/insight/trends` vs getting it from `/api/dashboard/id` as on first load.

Relates to #3609  

#### *Thank you* for your bug report – we love squashing them!

posthog/api/dashboard.py
result = serializers.SerializerMethodField()
    last_refresh = serializers.SerializerMethodField()
    _get_result: Optional[Dict[str, Any]] = None
    class Meta:
        model = DashboardItem
        fields = [
            "id",
            "short_id",
            "name",
            "description",
            "filters",
            "filters_hash",
            "order",
            "deleted",
            "dashboard",
            "layouts",
            "color",
            "last_refresh",
            "refreshing",
            "result",
            "is_sample",
            "saved",
            "created_at",
            "created_by",
        ]
    def create(self, validated_data: Dict, *args: Any, **kwargs: Any) -> DashboardItem: