Debugging the optmization run while training variables of a pre-trained tensorflow model

I am loading a pre-trained model and then extracting only the trainable variables which I want to optimize (basically change or fine-tune) according to my custom loss. The problem is the moment I pass a mini-batch of data to it, it just hangs and there is no progress. I used Tensorboard for visualization but don't know how to debug when there is no log info available. I had put some basic print statements around it but didn't get any helpful information. And the model is from this repository: The problem is with training i.e. the last step.