[Height of Labeltext for X-Axis]

Dear Luzia. Unfortunately, Chart FX API does not provide a property to customize Label text area height. You should reduce the text you are currently sending to axis labels. As a workaround, you can change label angle (chart1.AxisX.LabelAngle = 45;). I hope this helps.

[Zoom in a chart causes some lines disappear]

Dear Xiaonan Ji. You need to use XY chart to avoid this behavior. Unfortunately, Chart FX engine will draw only lines between visible points inside the zoomed area.