I was using the Pentaho Update Step with “Use Batch Updates” in the PDI Community Edition 4.3.0 with error reporting configured and the commit set to 100.
The transformation was updating a timestamp, a processed marker ‘Y’ and a description column.
The Update log confirmed that all rows were processed in an Excel Output File, but the job stopped updating at 9100 rows with no errors reported.

The fix was not to: “Use Batch Updates”