Debugging tips for "System.NotSupportedException: Specified method is not supported"

[dchege711]

Is there a recipe for debugging the root cause of errors like:

System.NotSupportedException: Specified method is not supported.
   at ProtoBuf.Grpc.Internal.Proxies.ClientBase.IMyFooService_Proxy_0.IMyFooService.BarAsync
   at Contoso.Foo.FooClient.RunBarAsync

I've tried numerous things, e.g., dropping DateTimeOffsets from my contract, double-checking definitions, etc., and it feels like I'm throwing things at the wall to see what sticks.

Where can I find more information on why IMyFooService.BarAsync is not supported? Even with a debugger, I cannot step into IMyFooService_Proxy_0, which makes it hard to know why the method is not supported.