Table reorganize background process is "stuck"

Over 24 hours ago I started a table reorganize process on a very large table by performing a "alter table ... partition by...reorganize" operation. Data has been shuffling over all of my nodes since then. Disk space fills to 100% on each node and immediately falls back to normal levels. Data shuffling has now stopped, querying partition_status shows that the partition_reorganize_percent is still zero. Querying the partitions view shows all partition_key values have been set to null. No errors appear in the reorganize_errors view. How can I ensure that this reorganization operation completes?