The Cluster service is shutting down because quorum was lost.

You may witness that a SQL Services on a cluster you have maintained failed over to another node unexpectedly. You might see the below error.

"The Cluster service is shutting down because quorum was lost."

You then try to troubleshoot and you will come across series of errors as below.

"Cluster node '' was removed from the active failover cluster membership. The Cluster service on this node may have stopped. This could also be due to the node having lost communication with other active nodes in the failover cluster. Run the Validate a Configuration wizard to check your network configuration. If the condition persists, check for hardware or software errors related to the network adapters on this node. Also check for failures in any other network components to which the node is connected such as hubs, switches, or bridges."

"The Cluster service is shutting down because quorum was lost. This could be due to the loss of network connectivity between some or all nodes in the cluster, or a failover of the witness disk. 
Run the Validate a Configuration wizard to check your network configuration. If the condition persists, check for hardware or software errors related to the network adapter. Also check for failures in any other network components to which the node is connected such as hubs, switches, or bridges."

"The Cluster Service service terminated with the following service-specific error:
A quorum of cluster nodes was not present to form a cluster."

As you can see in the event error itself, the Cluster Service lost the quorum and since it was unable to find the quorum, it infact dint actually failed over your services rather, it complete shutdown the cluster service itself.

Once the Quorum was back again, the services were moved to best possible node on a cluster. This has nothing to do with SQL Server, rather, its something to do with the storage and you need to investigate with storage so as to why the Quorum Disk was lost.

Hope this information was helpful