Handling Incipient Failures in SAFe
In Scrum, there is the notion of Cancelling a Sprint and returning to Sprint Planning if the Sprint Goal becomes obsolete, or if the iteration plan is so far off base that scope can't be renegotiated without obviating the current Sprint Goal. However, I can find no parallel mechanism in SAFe 4.x that provides a similar escape hatch.
Given a Program Increment (PI) with goals that teams discover can't be met during the course of the PI, or Sprints/iterations within a PI that need to be replanned (not just re-scoped), what is the framework mechanism for doing so? While you're allowed to renegotiate scope in SAFe, sometimes that isn't enough to actually meet a goal; sometimes objectives or plans need to change, too!
Obviously teams can replan at iteration boundaries within a PI. There are also opportunities to introspect issues and improve planning in the future during the Inspect and Adapt (I&A) or Innovation and Planning (IP) cycles in SAFe. However, the notion that the Agile Release Train (ART) just keeps chugging along, even once it's discovered that the train is headed full-steam down the wrong track, seems fundamentally wrong to me. What have I missed or misunderstood about this aspect of the framework?