RobotStudio event

Pick place drifting in IRB 340 Delta Robots.

I have a Dual Delta Robot application using irb 340 controllers.  We have had them in place for approx 10 years.  We are doing a case packing application where it picks up packages and places them in boxes.  We use a photo eye to determine leading edge of the package.  Recently, as it is running, the pick point has been "drifting" at higher speeds.  Instead of picking the package in the middle of the package, it starts to creep towards the trailing edge of the package.  This is only happening in the first of the two robots.  A hard power cycle seems to be the only thing we have found at this point to "fix" the problem.  

Any thoughts would be greatly appreciated.

Ken