To understand the root cause of the issue, I'll recommend you open a case with netapp support and provide the nessary data.
and they should be able to help you identiy the reason for failure of both controller (HA Pair)
Mean while you can make sure few things using the following commands.
::> set adv
::*> node show
::*> cluster show
::*> cluster ha show
::*> cluster ring show
::*> cluster kernel-service show
::*> cluster ping-cluster -node node-01
::*> cluster ping-cluster -node node-02
::*> system health status show
::*> system health alert show
::*> system health subsystem show
::*> system health config show
::*> system environment sensors show
::*> system node power show
::*> storage failover show
::*> storage failover hwassist show
::*> storage failover interconnect show
::*> event log show -time >= 1h
Still I highly recommed you to open a case with netapp support to get the bottom of it.