Boeing was just recovering after getting 200 MAXs returned to service since December and while this latest manufacturing flaw is unrelated to the flight-control system implicated in two fatal crashes that grounded the MAX for nearly two years, it slows the positive momentum that had begun to build as more MAXs took to the air and new orders came in.

The problem has been caused by a backup electrical power control unit which was secured to a rack on the flight deck with fasteners instead of rivets. Apparently, this was done in such a way it did not provide a complete electrical grounding path to the unit.

This could cause malfunctions in a variety of electrical systems, such as the engine anti-ice system and the auxiliary power unit (APU) in the plane's tail.

This time Boeing spotted the issue "on a production airplane during normal build activity" and that inspections are needed to verify "that a sufficient ground path exists" for this control unit.