Solution
This issue happened because based on the original VI, instead of comparing properties of the XML documents, it actually comparing the XL refnum (memory). Even though the node is the same, the refnum for the probed nodes are different because they are two different items being opened at the same time.
Insert an Invoke Node: Get XML function to each probed node before comparing them. After adding the Invoke Node functions, the probed nodes will actually compare the attributes of the XML documents instead of comparing their refnums.
After this addition, when comparing the two nodes, it will give out a TRUE value.
