Possessed unique map boss in ritual

Hi!
The Cross Contamination league challenge says "Defeat a Unique Map Boss that is Possessed while in a Ritual".
I went into an Alleyways map that had the mod "Unique Bosses are Possessed", then pulled the boss to a ritual somewhere else on the map, started the ritual, and killed it during the ritual, yet I didn't get the challenge.
Is this intended?
If it's intended to not give the challenge in this situation, would it be possible to clarify the text on the more exact circumstances people need to achieve?
Thanks!

I too just had this same problem. I brought the map boss from cemetery into 4 rituals and nothing.. help?

If this is the same as in previous leagues, then you need to do it via a Haunted Ritual encounter, which is rare. This was never made clear previously either. That's how I did it last time.