Hi Hassan,
Thanks for contacting Syncfusion support.
Currently, we have not included the ReportViewer support in ASP.NET Core platform. We have already completed the ASP.NET Core support for ReportViewer control and it is planned to be included in our Essential studio 2018 volume 1 main release, which is tentatively scheduled to be release by this week. Also, we have unclear about the mentioned ReportViewer issue in ASP.NET Core platform. So can you please share the brief detail of the issue to validate the mentioned problem at our end.
Regards,
Yuvaraj D.