Failed to load expression host assembly. Details: Could not load file or assembly 'SSRSReportExtension'
Failed to grant permission to execute. (Exception from HRESULT: 0x80131418)
When selecting "New Report Template" SSRS does not launch in my staging tenant.
It had to do with a security feature that blocked full access to the .dll file since it was received from another computer. Once unblocked, previewing reports that utilize this extension will work as expected.