Welcome to the G!
It could be a lot of things, unfortunately. For example, the assembly inside could be slightly bent if the gantry was moved by hand, one of the bearings could be worn, etc. We had this within the first year of having the 8000, a long time back, and they replaced the entire gantry under warrantee. It never happened again, and ours has since been sold and found a new home.
If no one chimes in with additional suggestions, I think it might make sense to give the experts at Wizard a ring for this problem. They may even want to see/hear a video of the symptom, to help diagnose it.
Best regards,
Mike, Get The Picture Framing