Thank you for the attached code snippets, I was able to create a project based on this code. I had to alter a few things in order to compile and run the project. When I ran it the first time I saw an empty chart with no series in it. Then I commented one line and I did see a chart with two spline series (one on top of the other) displayed properly. When I hovered the mouse over the line - a tooltip showed up as expected.
I have attached the project in mind, for your reference. This is the line that I commented:
In the given context this series mapping does nothing so it is safe to remove it. Do try the attachment and let us know how it goes.
All the best,
the Telerik team