Right, there were repeated problems with the angle of attack sensor. If I had to guess the sensor itself is and was just fine and the problem lay elsewhere in the pipeline.
More important though is that the 737 MAX differs wildly from earlier 737s in how much it relies on the AoA data. Mechanics and pilots not experienced with the MAX were probably operating under the (false) assumption that a bad alpha vane wouldn't be the end of the world. In fact displays indicating the angle of attack and warnings about disparity between the alpha vanes is an optional feature on the 737. It's considered that unimportant.
The key differences from earlier 737s are that the MAX uses the AoA data to calculate airspeed and that the MAX may use a single AoA input to try to kill you. I believe the former was disclosed, but considered how short the differences training is may have been easily overlooked. The latter, of course, was not disclosed until the crash.
More important though is that the 737 MAX differs wildly from earlier 737s in how much it relies on the AoA data. Mechanics and pilots not experienced with the MAX were probably operating under the (false) assumption that a bad alpha vane wouldn't be the end of the world. In fact displays indicating the angle of attack and warnings about disparity between the alpha vanes is an optional feature on the 737. It's considered that unimportant.
The key differences from earlier 737s are that the MAX uses the AoA data to calculate airspeed and that the MAX may use a single AoA input to try to kill you. I believe the former was disclosed, but considered how short the differences training is may have been easily overlooked. The latter, of course, was not disclosed until the crash.