OK, this is roughly what I expected. In your failure case (#1), the process is failing without communicating with the server at all. It seems that the issue is isolated on your client, most likely in the specific user profile.
It seems possible that some part of the workspace state in your user profile has been corrupted, although this is not an issue that I have seen before. Assuming that this user is not set up for any other RemoteApp and Desktop Connections feeds, we can try the following. All steps are to be done while logged in to the client machine as the user who has seen the error.
1. In the registry editor, delete the contents of "HKEY_CURRENT_USER\Software\Microsoft\workspaces\Feeds\".
2. On the hard drive, delete the contents of "%USERPROFILE%\AppData\Roaming\Microsoft\Workspaces\".
3. Attempt to recreate the connection.