If you don’t specify the exact field, the default analyser configured against the default field in the index definition page under the “Advanced” section will be applied to the query parameters which would have text analysed them incorrectly.
Though the above comment is very valid in many such non working query cases, It isn’t quite right here with dateRange query as the date (start/end)parsing happens before inspecting the given query field. But here not giving the right field value creates empty looks up err later on. I am not getting into the specifics here which might not be very relevant to you.