UseProxyToSpaDevelopmentServer causing a lot of time to forward the request.
The raw webpack/ng serve server is pretty fast, should be processed within 100ms, but UseProxyToSpaDevelopmentServer API have to wait for 4 seconds to handle this request.
To Reproduce
Create a angular SPA project (based on .NET Core 3.1), modify the Startup.cs, change UseAngularCliServer to UseProxyToSpaDevelopmentServer and hit Ctrl+F5 to run directly(and run ng serve in front-end folder at same time).
Checkout the browser F12, should see this:

When using raw webpack/ng serve command without proxy(http://localhost:4200), performance is much better:

Further technical details
- .NET Core 3.1/3.1.100
- Visual Studio 2019(16.4.2)