The flight tracker shows a drop in altitude from 8,000+ feet to 7,000+ feet and then climbing to 9,000+ feet, that would have brought it dangerously close to hitting the ground since the surrounding elevation of the land is above 7,000 feet
The Lion Air 737 Max 8 also had extreme changes in pitch/climb rate. Something like 26 times in 10 minutes.
Apparently there's safety system that prevents the airplane from pitching up too sharply and will apply forward stick (nose down) to prevent a stall.
There is a way to disable the system, but in the case of Lion Air, the pilots didn't recognize the problem as being with the system, so they never disabled it.