C4W2E1 identity block

If those two exception segments are part of the same trace, then the error message is telling you that X_shortcut is (4,4,3) and X is (4,4,4). Which is the correct value? Why are they different?

Just as a side note here, you may want to consider reversing the order on that Add: it’s got nothing to do with your problem here, but it may save you trouble later. Please see this thread for more explanation.