A quote from
https://thepointsguy.com/news/boeing...re-on-landing/ :
Boeing did recently release a bulletin regarding the Thrust Control Malfunction Accommodation system (TCMA). The safety system is designed to prevent uncommanded high-thrust situations. In the bulletin, Boeing said that selecting full reverse too quickly upon landing before the aircraft has fully transitioned to ground mode could cause the system to activate. While this bulletin could shed some light on what happened, what actually caused the engines to shutdown won’t be clear until a full investigation is completed.