I am using 2D LineCharts and have multiple series defined in my XamChart. When there are too many data points, XamChart automatically adjusts the Units for my PrimaryX axes. Unfortunately, it doesn't put a valid DateTime Label, but lists the label on the axes as 'MM-dd-yy' and just shows 3 ticks.
I played around and found out that if I adjusted the number of datapoints to 28, it was working fine. But anything more than that would cause the PrimaryX axes to display 'MM-dd-yy'
You need to use Scatter or ScatterLine chart if you want to have DateTime values on the X-axis. In other case there will be just text labels.