[2022] New Eximus Rework Makes LVL 30+ Exterminate Riven Challenge Undo-able

I see some talk about Ivara, which is probably the easiest way to complete this riven unlock. Is there some bug where you're getting detected even though you're invisible? Or are people trying to use Sleep Arrow, and the eximus are ruining your plans because they're immune to it? It's otherwise not clear what strategy you used to be using that wouldn't still work