This is expected behaviour on a column series, and is due to having small dataset with a large range between the minimum and maximum datapoints.
In this case, the chart evaluates the maximum width of the columns it can display without overlapping. Due to two datapoint x value's being close together (2015-07-23) the columns have to be fairly thin in order to avoid a collision.
I'd recommend using an SChartDiscontinuousDateTimeAxis (please note this is a premium feature) which would enable you to remove the whitespace by skipping a date range, for example, 2015-07-24 to 2015-08-02. Our TimeSeries sample project demonstrates how to use the discontinuous axis if you'd like a bit more detail as to how it should be used.
I hope that helps explain it.