Solved by albanD in post #2 
              
              
                Hi, 
The problem is that in this for loop: https://github.com/tamarott/SinGAN/blob/e1384a9f6dfa45497f4aed5f3e52466d4200fcfb/SinGAN/training.py#L173 you reuse the same fake commputed with the original netG above. 
But when you do the first optimizerG.step(), then you modify the weights of netG inplac…