I have found that regardless of the value assigned to MajorLinesVisibility, CartesianChartGrid only draws horizontal lines.

Is there a way to make it show only vertical lines?

Hello Ian,

This is a known issue with vertical (x) major lines of RadChart on Android, we have it logged in our public portal, you could subscribe for receiving email notifications on status changes at the link below:
https://feedback.telerik.com/xamarin/1365960-chart-android-cartesianchartgrid-x-majorlines-are-not-showing

I am sorry for any inconvenience caused.

Regards,
Yana
Progress Telerik