I just tried to repro the bug, but couldn't. Maybe it was a transient issue? Anyways, here's what I remember when the bug occurred:
- The stage was 3x2
- The goal node was in the bottom left
- I think the level was level 7 or 8?
- When I reset the level to try again, the goal node in the bottom left turned into a singular conveyer with no connections
- Resetting the level again caused the goal node reappear
Hope that helps!