APAR PM80852: PBG GROWTH WITH APPEND=YES. ONLINE REORG PART DOES NOT RESET THE LAST PART NUMBER HAVING FREE SPACE WITH CONCURRNTLY RUNNING SQL.
Customer X experienced Partition-By Growth (PBG) size increase with APPEND YES. Assuming the data is sparsely distributed across the PBG partitions. The following ONLINE REORG redistributed the data to the first 3 partitions. However, after the SWITCH PHASE, concurrent SQL would still append data to the last partition, leaving many partitions empty in between.