Not disagreeing with your comment or disputing your video evidence - just wanted to note I managed to finally get that catalyst finished running wave at Alter of Sorrows. I also questioned why kills were not counting as you illustrated. I wonder if adjacent kill scores from the firefly effect, not the primary target itself, was what was working.
In either case the quantity of enemies bunched up and their low HPs seemed to finally do the trick for me. Also I did this in the past month or two for reference.
Good luck with it!
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Will give it a shot. Thank you!