Hi all
Glad to say that this has been resolved. In short, the Juniper side was specified with ESP having "noPFS".
With Endian, at least version 3.0.devel, it used IPSec version 5.1.1. Since IPSec version 5.0.0 and up, it's impossible to disable PFS. The Juniper side was altered and had PFS enabled, resolving the issue