It looks like there is an issue with the date time axis when using week interval units. I logged the issue in our issue tracking portal where you can track/comment and vote for the issue. Here is a link
to the issue. I updated also your Telerik points for bringing our attention to the issue. We will try to address it in one of our upcoming releases.
As you suggested, one option to work around the issue is to use TKChartCategoryAxis
Should you have other questions, do not hesitate to ask.
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