Solved by ptrblck in post #2 
              
              
                I guess you are reshaping the activation in the forward method of your model and might change the batch size to 1. If you are using x = x.view(-1, SHAPE) to flatten the tensor, then replace it with x = x.view(x.size(0), -1) which will keep the batch size and might raise a valid shape mismatch error…