I just got an InvalidOperationException with the message Async.FromContinuations was invoked multiple time" when using the AwaitObservable that takes only a single IObservable in FSharpx.Async 1.12.0
I found this commit which might be related, but I don't know if it is already in the current nuget package of FSharpx.Async 1.12.0.
I am calling AwaitObservable from within an Async returned by AwaitObservable that is still running. Might this be causing the problem? Are your tests covering that case?