Okay, so what I find is that I can keep adding line segments, change their attributes and UNDO just fine. Removing lines is where the issue is at, by disabling the groups, I found that the issue stems from the automatic push logic.
This logic activates the push when the number of curves or their length change differs between what’s referenced from Rhino and what’s recomputed in Grasshopper (basically pushing the wall outlines whenever I change any of the centrelines or their properties).
So now I am wondering if there is another method I could use, because as I mentioned, I want the wall outlines to update so I can draw my windows and doors with snaps.
I would assume a datadam to delay the push might work, but I can only really undo when I mash the undo button as fast as I can (as indicated by the line colour faintly flickering).