It might not help anything but this is why I’d try.

Disconnect the monitor from the power source.  Wait a few minutes to make sure it losses all of its memory.  Then hook it back up and re enter your speed cal, rows and row spacing.  

When we used one of those monitors years ago we had some crazy crap going on that we couldn’t figure out so we took it out of the tractor and to a dealer that had a test computer to hook it up to.   It worked fine when we got to the dealer and every day after that.   The only thing I could think of was that unhooking the power allowed it to clear its brain.