A test aircraft experienced an uncommanded pitch up or down event, eerily similar to the 737-MAX fiasco. This is said to push production out until at least 2024:

The Boeing 777X is allegedly facing serious certification issues, and it’s now unlikely any of these planes will be delivered before 2024.

Source: Uh Oh: Boeing 777X Facing Certification Issues | One Mile at a Time

The FAA is now keeping a close eye on Boeing as Boeing has lost the confidence of regulators after the 737-MAX disasters.

Coldstreams Skeptic