First question of course is, that how do you handle errors in your background step? What if the INSERT or function call (or how do you update the table?) does not work and returns sy-subrc NE 0 or error message? Do you at least get the error messages into the workflow log? If not, then your first and crucial step is to add the needed code/logic to the background step & workflow. Then just start waiting the error to happen and go investigate the workflow log.
If you already have the above mentioned logic at place (which you didn't mention), then this is a much more difficult case.
Kind regards,
Karri