Thanks for your interest in Syncfusion Components.
We have validated your reported scenario and we suspect that the problem occurs when you are specifying value for the parameter before report has been loaded. So, we suggest you set parameters in “ReportLoaded” event. We have prepared a simple report viewer sample based on your requirement and it can be downloaded from the below location.
If you still face problem, then please modify the above the sample to reproduce the problem at our end. It will be helpful for us to provide the solution at the earliest.