I am not sure what could be wrong. I am running a multilayer single item that I have used the array function to create many of the same object. When I run the file it will get through part of the way through the batch and somewhat randomly shift the alignment about 3mm to the left. I have been beating my head against a wall trying to solve this. It repeats but not in any way that is predictable.
I am leaning towards something to do with the steppers and belts but for all I know it could be software. Each time I am there everything works fine, but when I leave I get the shift.