While doing the force failover, the secondary node is undergoing a soft reboot and the NS is not getting failed over. 
WE can see the core files getting generated everytime we do a failover. 

The var/log/ns.log presents below records:
Nov 13 17:32:30 <local0.alert> NSAUSL nsppe: PE 0 (pid 1085) got signal 11; signal mask is 0x0 0x0 0x0 0x0
Nov 13 17:32:30 <local0.info> NSAUSL [27]: proc NSPPE-00 (1085) SIGNALED
Nov 13 17:32:30 <local0.alert> NSAUSL [27]: pitboss Mon Nov 13 17:32:30 2017 NSPPE-00 (1085) unexpectedly died due to receiving signal
Nov 13 17:32:30 <local0.alert> NSAUSL [27]: pitboss Mon Nov 13 17:32:30 2017 There may be a delay restarting process while collecting core dump on NSPPE-00 (1085)
Nov 13 17:32:30 <local0.alert> NSAUSL [27]: pitboss Mon Nov 13 17:32:30 2017 proc NSPPE-00 (1085) failure. Therefore initiating nCore NetScaler restart according to policy setting (0x29b4)
Nov 13 17:32:30 <local0.alert> NSAUSL [27]: pitboss Mon Nov 13 17:32:30 2017 NetScaler restart may be delayed if collecting core dump for NSPPE-00 (1085)
Nov 13 17:32:30 <local0.info> NSAUSL [27]: pitboss Mon Nov 13 17:32:30 2017 Nsshutdown sysctl lock remains free ...
Nov 13 17:32:30 <local0.alert> NSAUSL [27]: pitboss Mon Nov 13 17:32:30 2017 Pitboss declaring system failure: NSPPE-00 (1085) exited
Nov 13 17:32:30 <local0.debug> NSAUSL nsprofmon: Write failed because of broken pipe in nsnet_sendreq; FD=4 errno=32 peerPort=3010 peerProcess=nsnetsvc
Nov 13 17:32:30 <local0.info> NSAUSL restart[1576]: Attempting intial cleanup of netscaler daemons 
Nov 13 17:32:36 <local0.info> NSAUSL restart[1576]: Cleanup completed 
Nov 13 17:32:36 <local0.alert> NSAUSL restart[1576]: Nsshutdown lock released !

Workaround: disable the AppQOE and the AppFlow feature, however disabling AppFlow or AppQOE may cause issues with other entities like NMAS/Insight which uses AppFlow or AppQOE. Please verify the environment before disabling the same.
Fix: The Issue is fixed in 11.0 72+ release also customer can upgrade to 11.1 or 12.0 GA builds to have the fix for the same.

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Problem Cause

#697709 PE is crashing in the SSL handshake while doing ECDH key computation 

The issue reported on build 11.0 71.18 that the HA NetScaler reboots after an upgrade to 11.0 71.18 and generates a crash files while performing a force failover. The issue can also be seen at both the HA NetScaler crashing after upgrade to 11.0 71.18. Also it may cause several failover in the HA Environment.