I’m currently cruising in the Sydney region at M 0.81 at FL360. I set my autopilot to FL360, and it climbed to this altitude, but instead of easing down the nose to the cruise pitch, the autopilot is making the nose pitch up and down ±4 degrees at or around 36,000, almost like riding a bull, and thus never reaches FL360. I don’t remember this being an issue with “older” version of the 777-300ER autopilot.
Edit: Disconnecting and re-enabling the autopilot sort-of solved the problem. But I’m still curious as to why this occurs.