Alan,
Follow up on Waterford event.
Video:
https://youtu.be/Ai4AiWz7680
at 57 second on video you see the stacklight flash.
You also see our drivers struggle with that stack after restored.
FTA came to us with the issue, and mentor said one of the ATM fuses was not seated completely, he felt the fuse move, and seat when he pushed on it.
As this was Finals Match 2, not much done after this to diagnose the issue.