A lot of false negative events

I've a lot of false negative events with count condition.

## Expected Behavior

No any triggered events.

## Current Behavior

This event occurs several times a day.

## Possible Solution

Fix the problem/

## Steps to Reproduce (for bugs)

Condition Type: Filter & Aggregation
Search Query: *
Search within the last: 30 minutes
Execute search every: 10 minutes
Aggregation of results reaches a threshold
If `count()` Is `<` Threshold `1`

## Context

The problem didn't exists before upgrade to graylog 3.

## Your Environment

* Graylog Version: `3.1.2 (graylog/graylog:3.1)`
* Elasticsearch Version: `docker.elastic.co/elasticsearch/elasticsearch-oss:6.8.3`
* MongoDB Version: `mongo:4.0`
* Operating System: Docker on Ubuntu 18.04
* Browser version: Netscape navigator