I noticed a lot of entries of that type in /var/log/vsmagent.log.
From what I can tell, process 123 indeed doesn’t exist anymore, for a good reason: it corresponds to the previous tl-session, which from a user perspective ended as expected.
The log entry seems to be generated by an obfuscated /opt/thinlinc/modules/thinlinc/vsm/handler_verifysessions.py.
What could be reasons for ThinLinc believing that the previous session should be alive?