New version since what?
The last major change to Numbers was 14.4, which added a number of array-based functions that changed how some formulas worked (e.g. they'd return a range of cells rather than a single value), and there's been much discussion over them, and how to reconcile the differences.
If you're talking about upgrading to the latest 15.1 version, there are no significant formula changes from 14.4, so whatever worked then should continue to work.
You're also lacking details of what does happen now. Do you get any value? an error? the wrong/unexpected value? that could be key in tracking down what's going on.
It might also help to show the formula you're using. It's also worth noting there are several ways of 'getting the last value in a column. My personal favorite is TAKE():
=TAKE(TOROW(B,3),1,−1)
This first converts all the values in column B into an array (while skilling blank and error cells), and then takes the last item, but there are other options, too.