Hello Christian,
thank you for your suggestions. The user name was logged too, but the users could not recall what exactly they did at that time and we could not reproduce the log entry. It seems like in this case the Illuminator is called directly, so no entries in the Transaction Manager or in SAP as it was only a query on the local MII database.
But your suggestion with the logging path was useful. I changed the log setting for com.sap.xmii.Illuminator.tools.database.DBQuery to INFO and now all the queries are written into the log. It is a big quantity of entries, but the load of the MII system seems to stay more or less the same. I will check if the relevant log entry is also created when the error occurs.
Best regards,
Gernot