Things move fast in the world of deep learning. During the 8 months the paper associated with this repository was in review, Tensorflow and Keras libraries underwent some major changes. Tensorflow did a major upgrade from version 1 to version 2, and keras got subsumed as into Tensorflow as tf.keras.
This is the version of the software that worked in October 2019 prior to the official release of Tensorflow 2, and may be used to exactly reproduce the results of the paper, if you can get it to work using tensorflow 1.X. This release version will not work in tensorflow 1.X.