Thanks Lynn. Was gardening all day yesterday and some this morning and finally got to watch the machine very closely. Checked everything you listed to no avail.... but while watching I noticed the board "jumped" ever so slightly as it was moving left to right and the error then appeared.
Took the board out and looked at it very closely... the board on the keyboard side was not perfectly flat. Though it was square in all 4 corners, there was a very slight <0.5 mm (perhaps 3 inch long) convex bow in the middle of the 28 inch maple board. I tried another maple board and it worked. Since then I have got one more pattern to run fine.
I appreciate everyone's help and also apologize for "blaming" the machine and not checking my board more closely than I did.
I will also double check the head pressure!