Re: SRX 3400 in Cluster config is synced but new configuration is not applying

This looks like your cluster is not healthy because of communications channels between the devices.  You can verify this by looking at:

show chassis cluster status

show chassis cluster interfaces

http://www.juniper.net/techpubs/en_US/junos/topics/reference/command-summary/show-chassis-cluster-interfaces.html

And confirm the interface use and cabling for the cluster matches the setup for the SRX3400

Configuration confirmation

https://kb.juniper.net/InfoCenter/index?page=content&id=TN10

Troubleshooting steps

https://kb.juniper.net/InfoCenter/index?page=content&id=KB20641