After Training, I saved Both Keras whole Model and Only Weights using
model.save_weights(MODEL_WEIGHTS) and model.save(MODEL_NAME)
Models
This is probably due to a model saved from a different version of keras. I got the same problem when loading a model generated by tensorflow.keras (which is similar to keras 2.1.6 for tf 1.12 I think) from keras 2.2.6.
You can load the weights with model.load_weights and resave the complete model from the keras version you want to use.