server 2012 r2 Virtual Machines "unidentified network"

Host is Server 2012 R2. 

Guest: Server 2012 R2

Network become unidentified network suddenly on a VM guest, Same Host another VM guests work normally on same Virtual Network card.

I changed Virtual network to another internal virtual network card the network services resume normal. 

I 'm afraid another VM guest will become unidentified network  suddenly.

Any suggestion?

Thanks.