I cannot reproduce the issue using:
model = decoderNW()
x = torch.randn(2, 32)
out = model(x)
out.mean().backward()

but also needed to modify your model in:
        self.FC1 = nn.Linear(channels, 1024)

        self.FC2 = nn.Linear(1024, 10656)

as I didn’t know the input shapes for the desired reshaping.
Could you update the code with random inputs so that we could execute it and reproduce the issue?