I assume that ae_model is an instance of ConvAutoencoder.
If that’s the case, note that self.modelA will only use the child modules of ConvAutoencoder and will not apply the functional API calls in its forward such as torch.relu and torch.sigmoid and will also use the max pooling layer once.
nn.Sequential is a simple container to call modules in a sequential way. You could e.g. add the activation operations as modules (nn.ReLU() and nn.Sigmoid()) to the sequential model.
I think the better way would be to create a new model with the desired submodules and just call it in MyModel.