The accuracy is extremely low... even after changing a lot of options of Method...
Other methods' result is fine and normal, 0.80 accuracy like
NetTrain works well
I've tried several hours in Linux/Max/Windows version of Mathematica 11.3
Where goes wrong?
resource = ResourceObject["MNIST"]; trainingData = ResourceData[resource, "TrainingData"]; testData = ResourceData[resource, "TestData"]; trainSet = RandomSample[trainingData, 20000]; model1 = Classify[trainSet, Method -> "NeuralNetwork"]; cm = ClassifierMeasurements[model1, testData]; cm@"Accuracy"