I'm having the same issue. The best run I got was 10 hours then I get a call saying that it was missing its pick/place points.
At one point I thought maybe it was a duty cycle issue (i.e. the arm heated up & expanded) so we shut down the robot and then booted it back up after about an hour and it was still going to the same, incorrect points.
I marked off the pad locations on the base but it doesn't look like the robot has been jostled or moved.
At another point I thought that a crash had thrown off the encoders somehow but in this latest series of miss-picks/places the robot didn't crash before it started missing its points so that ruled that out.
Each time it misses, I always end up having to shift along the x-axis by 1-4 mm.
My theory right now is that since just about all of my positions are based on a landmark tag, maybe the fact that that's a variable plane is screwing with things (I am not actively using the landmark as part of daily operation I just have it there as a backup in case anything shifts so I can recover without a whole lot of effort). I just re-assigned the parent on all my points to the base frame (a static reference might help I'm hoping) but I won't know if that works for another 10 hours if history is any indicator.
Are you using the landmark system or are you using the base frame as the parent to your points?