One possible reason why each bar differs in size is because they get too shallow (~1.* pixels) and the framework starts rounding them to +- 1 pixel. If you stretch the timebar you will observe that the bars will become wider and no bars are missing, but again the system tries to round them.
You can try making the visible period smaller initially (perhaps a month). Another option could be to reduce the shown interval or increase the unit on which you show the bars from day to month for example.
All the best,
the Telerik team
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