The recurring messages that are seen are similar to these:
3/05 09:28:03.40 SDM125PRI domsrvr 19364 ERROR sec_mgr.c 3859 Unable to find DomSession 1645890540 used by user testUser1 invoked by domsrvr with reply method dob
3/05 09:28:03.42 SDM125PRI domsrvr 19364 ERROR domset.c 9950 dob_by_persid() failed for wf:6715345 (string)Unable to obtain DomSession 164589540
These messages may be an indication that the user identified in the first message has a session open with Service Desk that has been started but not touched for some time; when the user comes back to the session, it has already timed out.
There may be a pop-up message displayed on the user's system, possibly in a background window, indicating that the session has timed out.
Note that the DomSession identifier, 164589540, in the 2 messages in the example given above, match.
The user identified in the message needs to click on the 'OK' or 'Cancel' button that is in the pop-up window. This will end the session and instruct the user to login again.