After upgrading to the latest version 12.3.9+hf.1 you are experiencing multiple trace dumps caused by the error
U00005118 Program error: Database access via key 'EH_AH_Idnr' with value 0 in module 'UCDVAR_R'
This situation occurs if a DB event is terminated and still in status 1580 (=Resolving variables)
Release : 12.3.9
The issue has been confirmed to be a bug and will be fixed with a future service pack for Automation Engine V21.0.