In various places of NoesisGUI plugin sources, /Game/ prefix is hardcoded, meaning the asset is presumed to reside under the Content folder of Project, however it does not work for ones in Plugin's Contents, notably these ones:
https://github.com/Noesis/UE4Plugin/blob/master/Source/NoesisEditor/Private/NoesisXamlFactory.cpp#L341
https://github.com/Noesis/UE4Plugin/blob/master/Source/NoesisRuntime/Private/NoesisResourceProvider.cpp#L34
https://github.com/Noesis/UE4Plugin/blob/master/Source/NoesisRuntime/Private/NoesisResourceProvider.cpp#L63
https://github.com/Noesis/UE4Plugin/blob/master/Source/NoesisRuntime/Private/NoesisResourceProvider.cpp#L79

(1) I would recommend the argument being passed into LoadXAML() function be just the xaml asset name, and by using AssetRegistry, a FAssetData could be fetched based on that name as the key. Then that FAssetData could be converted to UObject*, in our case as UNoesisXaml* as noted here:
https://docs.unrealengine.com/en-US/ProgrammingAndScripting/ProgrammingWithCPP/Assets/Registry/#convertingfassetdatatouobject*

That operation actually also invokes LoadObject() under the hood.
https://github.com/EpicGames/UnrealEngine/blob/master/Engine/Source/Runtime/CoreUObject/Public/AssetRegistry/AssetData.h#L248

That way, we would not have to preprocess the path with /Game/, regardless of where the asset resides, either in Project's Content or Plugin's Content folder.
Besides, it would be great if you could make the loading asynchronous as recommended here in case we have numerous xaml asset widgets:
https://docs.unrealengine.com/en-US/ProgrammingAndScripting/ProgrammingWithCPP/Assets/AsyncLoading/index.html

(2) Otherwise, it looks like in here:
https://github.com/Noesis/UE4Plugin/blob/master/Source/NoesisRuntime/Private/NoesisXaml.cpp#L13
We could pass the UE asset path as it is directly like these:
Noesis::GUI::LoadXaml(TCHARToNsString((GetPackage()->GetPathName())).Str());
Noesis::GUI::LoadComponent(Component, TCHARToNsString((GetPackage()->GetPathName())).Str());

If so, that path could be forwarded to FNoesisXamlProvider::LoadXaml() and fed well to LoadObject, without having to use AssetRegistry I guess.