You could reverse the order of the data (put the new data into Concatenate 0). I tried one where I find out how many lines are in the text window and set the scroll property so that you are always looking at the last line. There is a bug in LabVIEW (and yes, I reported it to NI) where the scroll position is set/reported incorrectly. If you have a text box with 4 lines, the scroll position is reported as 0, 1, 2, 2. there is no fourth position (the last two positions are always the same number).
So, I would say, that you should reverse the order of the data.