I’ve been trying to pinpoint the issue.
I think it might have something to do with the small incremental waterfall steps.
In my fiddle, if I change the y value of the 3rd data point from -102198 to -1021980 (adding a zero), the indexLabels render correctly.
Same if I add a zero to the end of the 2nd data point.
It seems that having incremental values that are a certain level smaller than the first and last waterfall bars is causing the issue. Any known remedy to this?