RestNet | RestNet-50 Model using Tensorflow | Machine Learning library

First of all, I know that there is a similar thread here: https://stats.stackexchange.com/questions/352036/what-should-i-do-when-my-neural-network-doesnt-learn

But unfortunately, it does not help. I probably have a bug inside my code which I cannot find. What I am trying to do is to classify some WAV files. But the model does not learn.

At first, I am collecting the files and saving them in an array.

Second, create new directories, one for train data and one for val data. Next, I am reading the WAV files, creating spectrograms, and saving them all to the train directory. Afterward, I am moving 20% of the data from the train directory to the val directory.

Note: While creating the spectrograms I am checking the length of the WAV. If it is too short (less than 2 sec), I am doubling it. Out of this spectrogram, I am cutting a random chunk and saving only this. As a result, all images do have the same height and width.

Then as the next step, I am loading the train and val images. And here I am also doing the normalization.