Please compare reference designators of components in Schematic and PCB. Change them if necessary. Then renew layout from schematic by RefDes.
Thanks for the suggestion, Alex. That fixed the problem. I had not noticed that the RefDes had changed when I moved part of the schematic to a different sheet.
FYI- for each component where I had to put the RefDes back the way it was originally, the Schematic editor would warn me that another component with the same RefDes already existed, even though a search for the other RefDes turned up empty.
All OK now though. Thanks again.