1) If you have a firewall in between these servers which is patched with "Poodle sslv3 block" , its possible that the packets are dropped on firewall when Netscaler uses sslv3 for ssl handshake . Better disable sslv3 on the services forcing service monitors on tlsv1 .
2) backend server are over consumed with resources , and is rejecting some ssl connections .
3) backend servers have multiple interfaces , and some return traffic are not routed back to Netscaler as its taking a different interface and looping in your network .
Monitoring HTTPS gives error - Time out during SSL handshake stage
in Core ADC use cases
Posted
1st Option fixed my issue, Thanks.