I would love to get a response to this specifically. My experience has been the same as pre's, where the agro table needs to clear before a tag change can occur. If this is specific to Azuregos then I think we understand what is going on, if not then something is broken somehow.
I have a video that directly contradicts this. You can see in the following clip our entire raid is wiped except one person who is out of combat with Azuregos. Azuregos is still in combat with many alliance yet the tag is still assigned to our raid group. Roughly 41 seconds into the video, well after our raid is completely off the agro table, the boss magically switched.
Here is the video showing Azuregos switching:
Here is a video showing how every other mob's agro table works: https://youtu.be/5q9IBO7pNgo