C# Interactive "Alt + Enter" broken since 16.8.x

Version Used: C# Interactive 3.9.0-6.21124.20 VS2019 16.9

Steps to Reproduce:

1. Open VS2019 then open C# Interactive Window.
2. Type some class name that is not of System namespace, because System namespace is default using. For example type ipaddress, case insensitive.
3. Press Alt + Enter.
4. It does nothing here.

Expected Behavior: After press Alt + Enter, it will ask you whether using System.Net, if I press enter again, it will auto complete the using System.Net; and auto convert ipaddress to IPAddress like the following image. In VS2019 16.7.x this is default behavior. Since 16.8.x it is broken!!!!!!!!

Actual Behavior: Nothing happen.