Don't let these EVA fans brain wash you. Yes, weather is a cause of turbulence but airline also contribute. EVA does not like their pilots to deviate from flight plan both in elevation and route. They are concerned about extra fuel burn and often just ride it out... It doesn't matter if the pilot in front of your fight reports in clear-air turbulence, it's up to your pilot to exercise discretion to change route or elevation. Risk-taking pilots often don't make the course adjustment because they have to ask tracon for permission and it's easiest just to ride it out, plus the plane is designed to thrown around.

There is a weather system off east of China, near Japan/Korea, it's always very very bumpy. It coincide with the meal service in long flights (either the departure meal or pre-arrival meal). EVA will leave the cart out in the aisle because it's a common path for them to leave TPE on but other airlines will suspend service if it gets too aggressive.

I fly this route at least one round trip every 2-3 weeks, and it's rare to remember a flight without turbulence, but something of this magnitude is less frequent. I do get enough of meal tray is bumped into the air from the tray table, so I usually hold down the cup that's holding liquid like red wine when I feel the turbulence is coming.

Just remember you keep your seatbelt on.. and tight! There is a reason they keep remind you of that. You especially need that with EVA.