Hi Bo, it's because of projected intersection snap - something like the top view of a helix when projected to 2D becomes a highly self intersecting curve and then the intersection calculation on that for getting an object snap spot can take a while to finish. MoI is most likely not crashed, just super busy crunching away generating a huge number of intersections.

Try going to Options > Snaps > Object snap options > "Use apparent intersections" checkbox - uncheck that and likely your problem will go away.

I have it on my todo list to try and make it possible for the projected intersection calculation to automatically give up if it is starting to take too long.

- Michael