Likely due to an inherent design flaw and/or the use of the BUAP in these plane incidents.

‘Don’t sink! Don’t sink!’ Pilot reports reveal at least 2 incidents of Boeing 737 MAX 8 nosediving
RT | Mar 14, 2019
https://on.rt.com/9q5t

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Boeing 737 MAX 8 pilots reported their planes nosedived and lost altitude in at least two incidents before the current safety scandal that has seen the aircraft grounded across the world.

As Boeing deals with the fallout of its Boeing 737 MAX 8 planes being banned around the world following two deadly crashes, reports of the aircrafts nosediving have been revealed while other reports cite safety concerns.

Pilots on at least two US flights reported their aircrafts nosedived and lost altitude quickly when using autopilot mode on the 737 MAX 8 in the last few months, according to pilot reports compiled in the Aviation Safety Reporting System database administered by NASA. The data shows there were 11 reports about the Boeing 737 MAX 8 logged between April 2018 and December 2018, USA Today reports.

In one incident, as soon as the captain put the plane on autopilot, the co-pilot said, “Descending,” and a cockpit audio low altitude warning said, “Don’t sink, don’t sink!” The pilots turned off autopilot and the plane stopped descending.