trigger_followup_campaign sometimes fails with "Non-active contacts can't be added to groups"

[toolness]

Here's the traceback:

Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/celery/app/trace.py", line 385, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/celery/app/trace.py", line 648, in __protected_call__
    return self.run(*args, **kwargs)
  File "/tenants2/rapidpro/tasks.py", line 26, in trigger_followup_campaign
    campaign.add_contact(client, full_name, phone_number, locale=locale)
  File "/tenants2/rapidpro/followup_campaigns.py", line 106, in add_contact
    self.add_to_group_and_update_date_field(client, contact)
  File "/tenants2/rapidpro/followup_campaigns.py", line 88, in add_to_group_and_update_date_field
    client.update_contact(
  File "/usr/local/lib/python3.8/site-packages/temba_client/v2/__init__.py", line 425, in update_contact
    return Contact.deserialize(self._post("contacts", params, self._build_params(**payload)))
  File "/usr/local/lib/python3.8/site-packages/temba_client/clients.py", line 63, in _post
    return self._request("post", url, params=params, body=payload)
  File "/usr/local/lib/python3.8/site-packages/temba_client/clients.py", line 358, in _request
    return super(BaseCursorClient, self)._request(method, url, params=params, body=body)
  File "/usr/local/lib/python3.8/site-packages/temba_client/clients.py", line 95, in _request
    raise TembaBadRequestError(errors)
TembaBadRequestError: Non-active contacts can't be added to groups