This will be tracked with updates by blancolirio [1] There was another youtuber starting a rumor that a child was in the pilots lap according to audio logs but AFAIK there is no public data to back this up so I would just wait for updates from blancolirio.
The reason given is uncertainty over deliveries, not performance. The 737-max and 787 are stacking up like chordwood in Washington because the FDA won’t release them