I noticed that for dbw tester, the dom-size-insight max children field was not getting a node element. There was a node id, but it pointed at the document fragment inside a shadow tree. The TraceElements saw it was not an element node, so it went to the parentElement. But since it's a shadow root, there is no parent element, and thus no node reference was created.

Instead, check if the element is a shadow root. If so, use its host.