I'm using sheet cam and Mach3 software is up to date.

I was cutting 0.5" in 3 passes, the shape was simple, a rectangle with two more rectangles inside. All in the same layer, sheet cam detected the interior lines and set an interior offset. I have done this before with no problems. The first interior rectangle was cut at the correct depth, the second rectangle is where it dropped to 1". Mach3 screen displayed 0.5" at the time. When the router retracted it only went up 0.5" and hit the material. I double check and everything was normal. What do you think happened?