Solved by ptrblck in post #8 
              
              
                I’m not sure how many samples your Dataset has, but probably the last batch is smaller than the specified batch_size. 
I would recommend to use the batch dimension flexible and rather specify the feature dimensions: 
x1 = x1.view(-1, 20)
x2 = pose.view(-1, 34)

This makes sure your code is also work…