RadarChartView the datas disappear when I enlarge or decrease the window

In my program inspired by ios demo
This is what happens

https://www.dropbox.com/s/r4bmn262esatiuf/screencast%202017-02-28%2010-31-41.mp4?dl=0

If in my program I put in comment the next line?

> yAxis.axisMaximum = 80.0

the problem is solved

> let yAxis = radarChartView.yAxis
> yAxis.labelFont = NSUIFont(name: "HelveticaNeue-Light", size: CGFloat(9.0))!
> yAxis.labelCount = 5
> yAxis.axisMinimum = 0.0
> //yAxis.axisMaximum = 80.0
> yAxis.drawLabelsEnabled = false
>

https://www.dropbox.com/s/n1vvg4e37m5psxv/screencast%202017-02-28%2010-33-20.mp4?dl=0

OK but why ??