Ritual encounter in Elder Guardian boss room can't be started after defeating the guardian

Hello everyone! I found a bug that appeared three times in my Elder Guardian maps when I can't start ritual encounter after defeating the final boss (guardian) and Maven's summoned other map bossess with Destructive Play passive in my atlas tree. The example of this bug is on the screenshot.

https://imgur.com/a/kVvDzEg

Is it my fault and it's not even a bug? It would be interesting to find out.

EDIT: It appears only in some Eradicatior and Enslaver arena layouts seems like.