Why doesnt activations() function work on regression output layer in a CNN imported from caffe using ImportCaffeNetwork?

Hi, I have a pretrained Image to Image Regression network in caffe. I have imported it into Matlab (2017b) using importCaffeNetwork(). I am using activations functions in matlab to visualize the output

activations(cnn30,imtest,'conv4','OutputAs', 'channels');

Where 'conv4' is the last layer. So activation of conv4 is my output image. but it gives following error.

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Assignment has more non-singleton rhs dimensions than non-singleton subscripts

Error in SeriesNetwork/activations (line 788)

Y(indices{:}) = reshapeFcn(YChannelFormat, numel(observationIndex));

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Interesting thing is that it works totally fine on layers above the last layer. for example same activations works fine on 'conv3' and returns a 96x96x8 array.

Plz help.