Hi Maurici,
Thank you for contacting Syncfusion Support.
We suspect that the refreshApppointments method is getting called before the scheduler renders on the page, which might cause such reported problem. We have prepared a simply sample, by calling refreshAppointments method of schedule within the button click event which can be downloaded from the following location.
Please check the above sample, and if you face same issue - kindly revert us with the details on which scenario or where you have called the refreshAppointments method and also if possible share the schedule code snippets too to proceed further on this.
Regards,
Nevitha.