WorldZone signal not matching Actual Robot Position

Tliford

I have set up a worldzone box above one of my presses to prevent the robot from moving in when the press door is open. When testing I noticed the signal was triggering at different times in the program seeming to drift or move. I pulled up the online monitoring and found that the digital position of the robot was getting ahead of the actual robot and the signal would trigger based on the virtual position of the robot. I have have waitDi's and fine point in the routine. 
Has anyone seen this before? 
Is there anyway to ensure they stay synced?