The last two changes I see to the script were line 103 where I added a check to skip inactive objects, and line 184 where I added the "#if UNITY_EDITOR" section, making it possible to execute the script via right-click in the inspector.
From there on, the changes include doing nothing in the Recenter() function if the transform.childCount is zero... and that's it, no other changes since February.
1. The script doesn't cache the list of children anywhere, but it does perform its logic in its OnEnable() function -- so maybe your order of execution simply changed (are you doing your child creation in some other OnEnable function?). You will want to call UICenterOnChild's Recenter() function after populating your content.
2. Sure. I'll add it -- however I'm going to make it a delegate member, not a static event.