Hi Joe,
I did some experiments to try to get the Profile Milling operation to stall out. I'm sure it's just a parameter that's set to something it's not happy with. I am able to cause it to stall out when Contour Z is set to the bottom of the canvas, 0%, which technically shouldn't produce any contours and error out. I'm not sure what I changed in v1.55b but it's not an issue on there - it just generates a blank toolpath and shows an error about it, but v1.53a definitely gets stuck calculating when contour Z isn't set to somewhere between the top/bottom of the canvas volume.
It's important that the operations which require the user set a contouring Z plane have it set to something that does produce a contour which includes the Profile Milling, Pocket Milling, and Medial-Axis Carving operations, otherwise they will either fail to generate a toolpath due to not having any contours at the set Z-plane or it can generate something undesirable.
- Charlie