I have the same issue on another iPhone 6 on iOS 9.0.2, and an iPad on iOS 9.1 (but only after it was Jailbroken and had Mobile Substrate installed, worked fine before that)
If I boot my Device into No Substrate mode the App works properly.
So the issue here seems to be with Jailbroken devices with Mobile Substrate installed (An essential piece of software to install tweaks after being jailbroken)
I don’t know how familiar you are with Jailbroken iDevices. And I know you probably don’t want to support them (this is the risk we take being jailbroken) but there does seem to be some incompatibility with WDliveApp and dylib versioning after jailbreaking. This issue does not affect any other apps on these devices.
It’s not the end of the world. I can live without the app, but I just wanted to let you know at this point what the issue is and for any others with Jailbroken iDevices having the same problem. A temporary solution is to boot into No Substrate mode (Hold volume up while powering on the device).