Can't Load a .Net Core 3.0 Web App Running From CLI

Issue:

I have a .Net Core 3.0 app that I'm unable to load in a browser ONLY when running it using the CLI, like so:

$ dotnet new webapp
$ dotnet watch run
watch : Started
info: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[0]
      User profile is available. Using '/Users/<user>/.aspnet/DataProtection-Keys' as key repository; keys will not be encrypted at rest.
info: Microsoft.Hosting.Lifetime[0]
      Now listening on: https://localhost:5001
info: Microsoft.Hosting.Lifetime[0]
      Now listening on: http://localhost:5000
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Development
info: Microsoft.Hosting.Lifetime[0]
      Content root path: /Users/<user>/Sandbox/coreapp3test

So everything looks good at this point, except when opening the URL in a browser I receive:

This site cannot be reached

localhost unexpectedly closed the connection.

Notes:

• I can run the app in VS Code, so the runtime must be installed correctly
• .NET Core 2.2 apps work fine with the CLI - I can run them from the CLI without issue. So it appears isolated to 3.0
• I've also tried the following, without success:
  • Removing bin/ and obj/ and restoring / building again
  • Re-installing the SDK - same result
  • Disabling firewall (in case that was blocking the connection)
  • Generating multiple web project types (e.g. angular, mvc, etc.) to see if it was related to the template

System Info:

$ dotnet --info

.NET Core SDK (reflecting any global.json):
 Version:   3.0.100
 Commit:    04339c3a26

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.14
 OS Platform: Darwin
 RID:         osx.10.14-x64
 Base Path:   /usr/local/share/dotnet/sdk/3.0.100/

Host (useful for support):
  Version: 3.0.0
  Commit:  7d57652f33

.NET Core SDKs installed:
  2.1.300 [/usr/local/share/dotnet/sdk]
  2.1.402 [/usr/local/share/dotnet/sdk]
  2.1.505 [/usr/local/share/dotnet/sdk]
  3.0.100 [/usr/local/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.4 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.9 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.4 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.9 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.4 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.9 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download