I recently tried to run one of our project in Visual Studio 16.2.4, and I'm now getting the following error:
IAsyncEnumerable exists in both System.Interactive.Async and mscorlib
We are referencing the System.Interactive.Async nuget package.
Unfortunately if I dereference the nuget package, it appears that while the type name is the same, the actual interface methods are quite a bit different. Additionally, there appears to be no equivalent for UWP, so the UWP build fails hard (shared project). Not only that, but because IAsyncEnumerable from the nuget package and from mscorlib differ in their definition, it is not possible to have shared code that is coded to a common interface.
Android has the same issue as iOS.