Solved by ptrblck in post #5 
              
              
                The output of the Bottleneck layer might be misleading: 
model.layer2[1]
Out[42]: 
Bottleneck(
  (conv1): Conv2d(512, 128, kernel_size=(1, 1), stride=(1, 1), bias=False)
  (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  (conv2): Conv2d(128, 128, kernel_size=…