I have some 100 or so XTend vb modules here, with xctu v6.5.0
It seems that updating firmware from 2004 to 2006 is rather problematic and temperamental.
I’m not sure which to consider, but I suspect that it is an XCTU issue, perhaps timing. It could also be a module issue, as pressing the reset in terminal mode gives a string of characters before generating the 9600 baud OK, taking a second or so.