https://arstechnica.com/information-technology/2019/04/boeing-delays-737-max-software-fix-delivery/

Delivery of Boeing’s promised fix to the flight system software at the center of two 737 MAX crash investigations has been pushed back several weeks after an internal review by engineers not connected to the aircraft raised additional safety questions. The results of the “non-advocate” review have not been revealed, but the Federal Aviation Administration confirmed on April 1 that the software needed additional work.