@ben ritter said:

Had the same issue in Layout 2017, but that just seemed to happen from one day to the next. Fixed it simply, but not sure why it happened.

BTW, what are PID's?

PID's are Persistent ID's. They are what allow dimensions in LayOut to be connected to the model and update automatically if you change the dimension in SU. If you delete a line or a point that is being used by a dimension in LO, though, the ID goes away and the dimension loses its connection.