After upgrading z/OS, the signon is failing and the transactions are running under the CICS default userid and failing with a security violation.
Can you please check to see if there is any Top Secret maintenance that was added that could be related and may have caused this process to break.
Release : 16.0
LU00851 is the only ATS related maintenance.
TSSUTIL reveals DRC E0 violation which is a PROTECTED attribute signon violation.
PROTECTED attribute was recently added to the acids receiving the DRC E0 which happen to coincide with upgrading their z/OS causing the signon failure.