## Bug description
I added an event (that exists) to an action, and now my action hangs forever.

I added an insight viewed event

w/ filters `insight == RETENTION` and `same_retention_and_cohortizing_event = false` – this appears to have broken my action where it does not load and I cannot edit it.

Cannot reproduce this same behavior locally.


## Expected behavior
- The action loads if the schema is correct.
-  If there's erroneous data it should load and let me edit it.

## How to reproduce

1. Create an action on Posthog cloud, in our main app
2. Add 'insight viewed' with filters `insight == RETENTION` and `same_retention_and_cohortizing_event = false`
3. The action will spin forever

## Environment

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

## Additional context

[Sentry error](https://sentry.io/organizations/posthog/issues/2378948964/?project=1899813&referrer=slack)

Console errors 
<img width="1607" alt="Screen Shot 2021-05-03 at 5 45 39 PM" src="https://user-images.githubusercontent.com/5965891/116950024-b0d7a280-ac38-11eb-93c8-245390240532.png">
<img width="1167" alt="Screen Shot 2021-05-03 at 5 51 34 PM" src="https://user-images.githubusercontent.com/5965891/116950026-b208cf80-ac38-11eb-96e1-6a8f018f650a.png">



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

ee/clickhouse/views/actions.py
team = self.team
        filter = Filter(request=request)
        entity = get_target_entity(request)
        current_url = request.get_full_path()
        serialized_people = calculate_entity_people(team, entity, filter)
        current_url = request.get_full_path()
        next_url: Optional[str] = request.get_full_path()
        offset = filter.offset
        if len(serialized_people) > 100 and next_url:
            if "offset" in next_url:
                next_url = next_url[1:]
                next_url = next_url.replace("offset=" + str(offset), "offset=" + str(offset + 100))
            else:
                next_url = request.build_absolute_uri(
                    "{}{}offset={}".format(next_url, "&" if "?" in next_url else "?", offset + 100)
                )
        else:
            next_url = None
        return Response(
            {
                "results": [{"people": serialized_people[0:100], "count": len(serialized_people[0:99])}],
                "next": next_url,
                "previous": current_url[1:],
            }
        )
def _handle_date_interval(filter: Filter) -> Filter: