We do not have an exact limitation of the count of the appointments, however, having too much appointments and resources can lead to some slowness while loading the control.
As to the resources I would suggest that you take a look at the Resources Paging
in our XAML SDK Repository - it demonstrates how you could implement paging of the resources in order to avoid loading all of the at once.
As to the appointments - you could load only the appointments from the current VisibleRange in ScheduleView as explained in our Load On Demand with RadScheduleView
Additionally, I'd ask you whether you have any customizations (custom Styles) or Special Slots in the control?
I'm looking forward to your reply.
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