i'm also having the same issue. while looking through the kii guides, i found on this page: http://documentation.kii.com/en/starts/unity/adding-kii-cloud-sdk-to-your-application/ ,
in the "Configuring your Project" section:
"Make sure they're included in your project properties as a referenced libraries (although Unity will load the dlls automatically if you drop them in the Assets hierarchy)."
i suspect his might have something to do with the stripping problem, and unity has this page on link.xml: https://docs.unity3d.com/Documentation/Manual/iphone-playerSizeOptimization.html
but i've yet to figure out what libraries to actually include to make unity stripping work with kii. if i use this in the link.xml:
<type fullname="System.Net.Configuration.WebRequestModuleHandler" preserve="all"/>
<type fullname="System.Net.HttpRequestCreator" preserve="all"/>
<type fullname="System.Net.FileWebRequestCreator" preserve="all"/>
the NotSupportedException changes to a "network related exception", but still i cannot login to the kii cloud. if kii can just provide the needed link.xml file, we may be able to make stripping work.