Both ACF2 and CICS have just been upgraded: CA ACF2 from v12 to v16; CICS TS from 2.3 to 4.2. Event Notification Facility (CAIENF) is running with the CICS component.
When ENF was enabled with "F ENF,MODE(CICS,NONE)" the abend is seen:
+DFHXS1103I CICSRGN Default security for userid CICSUSR has been established.
IEA995I SYMPTOM DUMP OUTPUT 181
SYSTEM COMPLETION CODE=0C4 REASON CODE=0000003B
CA ACF2 for z/OS R16
z/OS 1.11 (confirmed)
CICS TS 4.2