When using the automatic MQ-Table Reorganization (AUTOMATIC_MQ_REORG in UC_SYSTEM_SETTINGS set to 'Y'), some tables with LOB fields, created with the 'SECUREFILE' parameter, are not being reorganized. i.e.: MQMEM.
For more details on Oracle Lob-Segemtns please see: https://oracle-base.com/articles/misc/alter-table-shrink-space-online.
As off Oracle 12c LOB segments are created as SECUREFILE-LOBs by default. Hence, the automatic MQ-Table reorg doesn't work anymore as intended.
Release : 12.3
Component : AUTOMATION ENGINE
The issue will be fixed with a future ServicePack for Automation Engine 12.3 and newer.