Please confirm if one is facing issues with Default Switch connection on WINDOWS 10, 1809 Build 17763.1
Work around is to remove the VNIC on all the guests, start the VM so that the Guest OS does not recognize the VNIC. Shutdown the VM.
Add back the VNIC (Default Switch) and start the VM back.
Great!!!. This worked for me.
Am not sure if we have the same issue, my problem is that when I open the Hyper-V manager, and I try to creat a new extern Switch I get only one adapter and I can not find the deafult VM switch, the adpater comes and disapear so fast.