Thanks for your answer. Do you mean that I should delete the line with images = images.reshape(-1, input_size).to(device) and include  x = x.view(x.size(0), -1) in my “FeatureDatasetTrain”- and “FeatureDatasetTest”-class?
Because this gives me a new error: TypeError: 'int' object is not callable
I changed the input_size to 171 x 11 (–> (256 / 3 x 2) x11)