AMD Answer 73146
The processor might not output a Trace On packet in certain conditions surrounding System Error exception. Specifically, a Trace On packet is not output when the processor generates an asynchronous System Error exception element that is traced on a specific corner case while the trace is becoming active. The processor does generate the exception packet for this case.
This is a third-party errata (Arm, Inc. 856026); this issue will not be fixed.