Have people tried, like... moving earlier?

And I don't mean waiting for the cast. I mean, someone in the raid has a timer running, and if Twintania actually does cast it every minute on the nose, he warns people to start moving at 50 seconds (to account for voice chat lag/in-game delays, etc).

If five to ten seconds of advance moving still don't change a thing then you'll know for sure it's bugged, or there's something else to it than just moving.