I hope someone can help me figure out what's going on with my printer. I have been printing a couple of pieces and it's been printing perfectly. But for some reason every now and then, the printer moves down into the piece just before it finishes printing (after the final top layer) and completely wrecks the piece. I have no idea why this is doing it, and nothing I haven't changed the G-code since. to prove this, I printed an old model that I had on my computer, and it still managed to do it. Please help I have no idea why it's doing this.