Yes, I fixed the complex.

iD slows down after a few hundred edits in one session because it keeps track of the edit history for undo and redo. Slowdown due to loading in a lot of detail in one area is a separate issue.

The nodes are, as you say, like corners on the buildings. The buildings in and around Melba you were looking at were detected using computer vision (a kind of AI). I added them a few years back because they were better than nothing. I have improved many of them, but I haven't done much mapping in Melba so some of them are pretty poor. If I were mapping them today, I would have been much more selective with which ones were acceptable.