Somewhere, deep in the heart of an application, it would seem that an SQL Fetch has not been coded as it should have been. It's ending in error and the error isn't caught. In the job log a message says that the fetch returned more than one row. The result is that a letter destined for a particular client is not printed. If we try and run the same thing in a test environment, it works. It just occasionally doesn't work in production. We can see the program running the fetch in the log, but which instance of the program...
I'm running a tool to find all instances of Fetch in all rpg sources. I'll then look to see which ones are in the modules making up the program.
While I'm waiting for that to finish, maybe someone out there would have some clues about where to look, or watch out for.