Kalika is the only Mythic Troop available from Nexus as Nexus is a brand new Kingdom, so it will be the only Mythic Troop available in Nexus Event Chests until a 2nd Mythic is released for Nexus.
No coding was changed for the Event Chests New Mythics since maybe 2018? It has worked that way for a long time, but usually the event week Kingdom and the Kingdom the new Mythic Troop is from are different, which is why we hadn’t encountered this for a long time. If the Kingdom for the New Mythic and the Weekly Kingdom are the same, it will have the new Mythic exclusive in Event Chests as well.
The original post in the Spin me Right Round thread was edited when we saw confusion about AW and the Event Chests, so we edited the blog and the post on the forum so the information would be clarified there for anyone to see at the top rather than having to read the whole thread to see my reply clarifying.