Replacing filtered and or filter query with bool (Elasticsearch 5.2)

I forgot to mention: since you had the or part in a filter in the original query and you are not interested in scoring for this part, you should put it in the filter section of the overall bool query now. Combining the two clauses should work smothing like this:

...
"bool": {
      "must": { ... },
      "filter": {
        "bool": {
          "should": [
            {
              "term": {
                "severity.keyword": "ERROR"
              }
            },
            {
              "term": {
                "severity.keyword": "FATAL"
              }
            }
          ],
          "minimum_should_match": 1
        }
      }
    }
...