Native Plugin (.so) with dependencies not working in Editor mode, but works in Build (Linux)

Hello Unity wizards!
Can someone please tell me why my Native Plugin (trac_ik_wrap.so) loads in Linux Standalone Build, but not in Editor play mode. I have put all the dependencies of trac_ik_wrap.so in the Assets/Plugins folder. I have tried lots of different things like playing around with all the possible Import settings.
I always get this error: The type initializer for 'IK.trac_ik_wrapPINVOKE' threw an exception., which I think is a bit of red-herring as I’m pretty sure it’s a shared library loading issue (unless I’ve misunderstood the error message).
Project: https://github.com/Gregory-Baker/native-ik-plugin-test
Thanks,
Greg