Bars not rendering or disappearing while and after dragging

I've created a bar chart using BarChartView. The view displays work hours per day. Unfortunately, some bars are not rendered at all - and others are disappearing while the whole chart is dragged.

Before the chart is shown the first time, it's zoomed to show only 7 bars at a time:

barChart.zoom(scaleX:ceil(CGFloat(dataSet.xMax - dataSet.xMin) / 7), scaleY: 1, x: 0, y: 0)

Then the view is animated, so the latest day is shown first:

barChart.moveViewToAnimated(xValue: dataSet.xMax, yValue: dataSet.yMin, axis: barChart.rightAxis.axisDependency, duration: 0.8, easingOption: .easeInOutSine)

This leads to the following result - so far, so good:

As soon as I drag the chart to the right, bars begin to disappear - only the value remains visible (notice the bar of Mo. 6th - it's gone):

Also all bars which are further left and therefore not visible immediately (because of the zoom) are not rendered at all. What I' doing wrong?