We were on Deck 5 aft (5664) and they moved us to mid-ship deck 6 or 7 (I can't remember?). Our cabin on Deck 5 had an extra large verandah and the cabin they moved us to was an extra large room with a small verandah. They let us keep both cabins. We slept in one and used the verandah in the other. We noticed a huge difference. I won't book an AFT cabin on the Fantasy again and I love the AFT cabins on the Wonder. The CMs said the vibrations were worse than normal.
My parents were just in that room last week (May 12-19) and did feel the vibrations but it didn't bother them at all. And both of them are extremely prone to motion sickness.