Hi Phil, is it possible for you to send me the actual 3DM file through e-mail instead of just a screenshot? I can't debug a screenshot but if I can reproduce the problem over here with the actual file then I can work on debugging it or analyzing it to see what's going on.

Do you possibly have the history function kicking in? that's where if you edit some curves that were used for some operations when you edit those curves the operations will get recalculated.

Or also maybe you're running into an issue with intersection object snap where it can take a long time to generate the snap point on curves that are highly self intersecting when they are projected onto the 2D view's plane for doing an "apparent intersection" snap. You can test if that's the problem if it goes away when you disable the option for "Use apparent intersections" under Options > Snaps > Object snap options. I have that on my list of work to do to tune that up.

- Michael