Hi,
I can see where that trace is being created. The issue seems to be that you have blank values there. Could you activate security audit (transaction SM19) for this user and see what gets logged there. I can see that code write to security audit log and you might get more meaningful message there. Also do you see in trace message that starts with " IdP initiated SSO"? From brief look at code your message gets written to trace after user was successfully authenticated.
Cheers