Hi Dan,
I had something similar where my B1if database was growing at an abnormal rate and grew up to 40gb. What was happening was basically a scenario I built ended up creating a recursive loop and the scenario kept running over and over.
In my case I think it was because I had tried to change error handling in a scenario to run a specific scenario if an error occurred in processing. The scenario that needed to run was failing and essentially kept calling itself so the database kept growing because all of the messages associated with each call were being recorded.
The way I'd go about debugging would be
1) Use the TID monitor in the B1if Control Panel to find if there are any scenario steps that are being executed more than I'd expect.
2) Try turning off all scenario packages and see if the problem continues, then enable them one by one and see when the abnormal behavior starts.
3) If a problematic scenario is identified, figure out what in the process is causing it to behave differently from expected.
Regards
Cameron