Shadow Hunter Ultimate not Shadowmarking Nearby Enemies

Hello! I have been doing a lot of grinding lately on my shadow hunter and I realized that the ultimate, Arrow of the Goddess reads "Applies Shadowmark to all nearby enemies." However, when I activate my ultimate, it seems that no enemies get shadowmarked. It is possible that this is a visual bug that the mark is not showing, but the damage between an already marked enemy and one unmarked after my ultimate is not the same.

Thanks for reading, I hope someone can provide some insight into this issue.