When something worked once but an unexpected event occurs, it regresses back to a state of not working. Regressions are caused by bugs in the software due to new code being deployed into the existing code. While Revelry does a solid job of documenting, commenting, reviewing, and coding clean in general, regressions are also a natural part of software development.
When this happens, we treat the issue like a bug with high priority. The steps to reproduce are logged and we bring it to the top of the icebox to prioritize and work via the process. So if there was AC previously written and worked for the issue you are seeing, it is a regression.