Thank you very much for the answer @ptrblck. In train for Fashion MNIST, I have 10 classes. My result is in train:
Accuracy para la clase T-shirt/top: 0.85
Accuracy para la clase Trouser: 0.97
Accuracy para la clase Pullover: 0.90
Accuracy para la clase Dress: 0.90
Accuracy para la clase Coat : 0.76
Accuracy para la clase Sandal: 0.97
Accuracy para la clase Shirt: 0.61
Accuracy para la clase Sneaker: 0.95
Accuracy para la clase Bag : 0.97
Accuracy para la clase Ankle boot: 0.95
Accuracy promedio (balanceado): 0.88

If I train for CIFAR with no transfer learning, the result is the same.
Accuracy para la clase airplane: 0.69
Accuracy para la clase automobile: 0.78
Accuracy para la clase bird : 0.43
Accuracy para la clase cat : 0.48
Accuracy para la clase deer : 0.46
Accuracy para la clase dog : 0.57
Accuracy para la clase frog : 0.66
Accuracy para la clase horse: 0.70
Accuracy para la clase ship : 0.66
Accuracy para la clase truck: 0.69
Accuracy promedio (balanceado): 0.61

I take the learned model “best_model_FashionMNIST” and try to transfer learning for CIFAR problem. I get two classes as indicated above.
I will appreciate the comments
Greetings
K