The ES region contained the following configuration:
ES_JES_RESTART=Y
MF_UCC11=Y

The configuration above generated MFELX files for control of jobs in case of job re-start. The MFELX files were being retained and expected to be deleted on the execution of the spool housekeeping procedure.

However, the archived jobs' output files were removed from the folder but the MFELX files were still retained after the spool housekeeping was executed.

Full article: https://portal.microfocus.com/s/article/KM000016712