They added a tag to Shriekers named “can_summon” to circumvent the Warden from spawning upon certain criteria. This tag is automatically turned to false, if the player places a down Shrieker regardless of what mode. Meaning, the Warden cannot be summoned if the player has placed one down.
This is actually intended and not a bug.
I think they made this change intentional, so the Noteblocks trigger a Shrieker nearby, and doesn’t actually have to do with a puzzle.