Cannot post activity. Unauthorized

Question

For some reason, I am unable to start even the simplest bot in Bot Framework Emulator.

Steps to reproduce:

1. In VS2019, create new Echo Bot (Bot Framework v4 - .NET Core 3.1) project (using Bot Framework v4 SDK Templates for Visual Studio)
2. Run project without making any changes whatsoever (empty strings for MicrosoftAppIdand and MicrosoftAppPasswordin in appsettings.json)
3. Start Bot Framework Emulator

http://localhost:3978/ opens up in the browser without issue but in the Emulator I get the below errors:

Cannot post activity. Unauthorized.

POST 401 directline/conversations/<conversationId>/activities

What could be causing these errors with such a minimal project? My understanding is this should just work straight out of the box when running on localhost and no security credentials have been provided.

I am using a work computer and I'm wondering if there is something 'behind the scenes' blocking a connection somewhere/somehow? I have no idea where to look, though. It works fine on another computer and was working fine on this machine when I last tried a couple of months ago so I'm really confused.

Any clues or suggestions on how to debug this problem would be greatly appreciated.