I have a CFX-750 on RTX for guidance on my planter tractor. It always worked perfectly until a couple days ago. It started tracking 6 inches off. I went into the monitor and reset roll compensation adding 6 inches to it and everything worked correctly. Today it was tracking 6 inched off and I set back to the original setting and it is all good. The antenna has not moved. I've never had to do this before as it was right on. What happened?