There seems to be some inconsistency between the data in Untitled-2.jpg and the data shown in Untitled-1.jpg. From the rows of the data it is clear that all items should be evenly distributed. In the Sparkline the data is clearly not evenly distributed - it is very easy to see that the 4th and 5th points are closer than the 5th and 6th points are further away. So I suggest you investigate what is the exact data passed to the items source of the sparkline.
I have attached a simple project based on the data you provided that is displayed correctly.
the Telerik team