Microsoft released this KB for when Hyper-V virtual machines cannot be connected to sometimes when TCP connections reconnect in Windows Server 2012 R2.
Symptoms
This article describes an issue when TCP connections reconnect in Windows Server 2012 R2. A hotfix is available to resolve this issue. This issue occurs when Hyper-V virtual machines are running on a Windows Server 2012 R2 failover cluster.
A hotfix is available to resolve this issue.