Haven't you heard about the new augmented braking system ? It turns out that the brakes on the MAX are a little "grabbier" than the NEO so for certification reasons the MAX gooses the autothrottle a little bit three seconds after initial application of the brake to ensure that the feel is the same. Unfortunately dirt can sometimes get in the speed sensor, so it keeps applying thrust every three seconds until the pilot shuts down the power. Of course, this works whether or not the auto throttle is engaged, but there is a bit of string under the captain's chair that you can pull to engage the parking brake.
(Satire, of course.)