The GETXMLERRORMSG() function is not working when there are 2 or more input cards.
No error message (or output of any kind) would be returned if card number specified as the argument was greater than 2.
This has been identified as a product defect under APAR PM98089
WTX mapping rule GETXMLERRORMSG()
Diagnosing the problem
Known 'bad' XML does not produce any output from the GETXMLERRORMSG() function, and the input card argument is greater than 2.
Resolving the problem
Obtain and apply the fix for APAR PM98089