I would like to point out that I had the same issue with my CEM60. The problem was caused by iOptron changing their firmware so that it passes the mount alignment model between the mount and the any software connected to the ASCOM driver. The result was that the iOptron firmware was overwriting mount corrections being sent by SGP. Once I cleared the mount alignment model using the hand-controller, SGP was centering within 5 pixels every time.
I'm not sure if this is your problem, but if you are plate solving OK and the mount is not moving, this may be something to look into.
Fred