Report slow in IIS

We migrated from Windows Server 2008 (R2) to Windows Server 2016. We got new version of IIS that come with it (don't thing it matters in my issue). IIS version is 10.0.14393.0.

We have a report that is very slow want running in IIS. We have identified where it happens. It is in the report's Render method.

it takes less than 30 second calling the Render() in a standalone Windows App.

but it takes more than 3 minutes for the same thing.

Note, we design the report using SSRS but we only use the .rdlc in C#. using Microsoft.Reporting.WinForms' LocalReport class.

Anyone idea what can be the problem.

Thanks,

John