SQL Server 2012 Agent hangs at a particular time of the day There is a 3 node SQL Server Failover Cluster with 3 instances running on same node at the moment. SQL Server version is 2012 with SP3.

At a particular time of the day at 4 PM daily, SQL Agent hangs and following error comes in SQL Agent Log:


  2019-12-17 20:17:53 - + [260] Unable to start mail session.
  
  2019-12-17 20:17:53 - + [396] An idle CPU condition has not been
  defined - OnIdle job schedules will have no effect
  
  2019-12-17 20:17:53 - + [408] SQL Server XXXXXXXX is clustered -
  AutoRestart has been disabled
  
  2019-12-18 16:20:30 - ! [298] SQLServer Error: 65535, SQL Server
  Network Interfaces: Error Locating Server/Instance Specified
  [xFFFFFFFF]. [SQLSTATE 08001]
  
  2019-12-18 16:20:30 - ! [165] ODBC Error: 0, Login timeout expired
  [SQLSTATE HYT00]
  
  2019-12-18 16:20:30 - ! [298] SQLServer Error: 65535, A
  network-related or instance-specific error has occurred while
  establishing a connection to SQL Server. Server is not found or not
  accessible. Check if instance name is correct and if SQL Server is
  configured to allow remote connections. For more information see SQL
  Server Books Online. [SQLSTATE 08001]
  
  2019-12-18 16:20:30 - ! [382] Logon to server 'XXXXX\XXXXXXX' failed
  (ConnUpdateStartExecutionDate)
  
  2019-12-18 16:20:31 - ! [298] SQLServer Error: 65535, SQL Server
  Network Interfaces: Error Locating Server/Instance Specified
  [xFFFFFFFF]. [SQLSTATE 08001]
  
  2019-12-18 16:20:31 - ! [298] SQLServer Error: 65535, SQL Server
  Network Interfaces: Error Locating Server/Instance Specified
  [xFFFFFFFF]. [SQLSTATE 08001]
  
  2019-12-18 16:20:31 - ! [165] ODBC Error: 0, Login timeout expired
  [SQLSTATE HYT00]
  
  2019-12-18 16:20:31 - ! [165] ODBC Error: 0, Login timeout expired
  [SQLSTATE HYT00]
  
  2019-12-18 16:20:31 - ! [298] SQLServer Error: 65535, A
  network-related or instance-specific error has occurred while
  establishing a connection to SQL Server. Server is not found or not
  accessible. Check if instance name is correct and if SQL Server is
  configured to allow remote connections. For more information see SQL
  Server Books Online. [SQLSTATE 08001]
  
  2019-12-18 16:20:31 - ! [298] SQLServer Error: 65535, A
  network-related or instance-specific error has occurred while
  establishing a connection to SQL Server. Server is not found or not
  accessible. Check if instance name is correct and if SQL Server is
  configured to allow remote connections. For more information see SQL
  Server Books Online. [SQLSTATE 08001]


Also if I query sp_readerrorlog through ssms, following error comes:


  Msg 22004, Level 16, State 1, Line 0 Failed to open loopback
  connection. Please see event log for more information.
  
  Msg 22004, Level 16, State 1, Line 0 Error log location not found.


I have found the same symptoms in the support page of Microsoft:
https://support.microsoft.com/en-in/help/3185365/sql-server-2016-agent-fails-to-start-or-failed-to-retrieve-data-error

But the above issue in the Microsoft Support Page is for SQL Server 2016, where the resolution is to update the ODBC Driver 13.1

But in my case it is SQL Server 2012, and in ODBC Data Source > Drives - no ODBC version is to be found other than Native Client.

This issue is occurring only on one of the instance among the total 3 clustered instances on the server.
We had similar issues on one of our clusters and found that "Allow the computer to turn off this device to save power" was turned on for the primary NIC. Id try turning that setting  off on any/all NICs. I posted as "a possible" answer so I could post the picture: