Hi, I’m far from expert but a simple thing to try is to print the output tensor before the second pooling by applying sum() on filters so as to quick spot if there are all zeros. You can do that by using this shortened forward function instead:

> def forward(self, x):
        out = self.conv0(x)
        out = self.relu(self.conv1_1(self.pad(out)))
        out = self.relu(self.conv1_2(self.pad(out)))
        LL = self.pool1(out)
        out = self.relu(self.conv2_1(self.pad(LL)))
        out = self.relu(self.conv2_2(self.pad(out)))
        LL = self.pool2(out)
        return out, LL


Then analysis out and LL.
Hope it helps.