A second KNX Virtual session cannot be used.
Indeed, ETS connects to KNX Virtual via the IP localhost (IP address 127.0.0.1) and uses the default IP port 3671, KNX Virtual uses the same default IP port, in order to open a second KNX Virtual session a different IP port shall be used (e.g. 3672).
Since KNX Virtual uses the IP localhost (IP address 127.0.0.1), it could be that installed Antivirus and/or Firewall disables it.
Make sure to add KNX Virtual to the 'safe software' policy of this installed Antivirus and/or Firewall.