As far as I understand it Arcadia has a problem with her azipod system. The reason they are keeping the speed down is that if they cruise at full speed it causes vibration which can be unpleasant for the passengers. I believe the ship goes for a re-fit in November. Until then the amount of time in some ports, not all, has been reduced.
We returned from a cruise to the Norwegian fjords on Arcadia on 3rd August;, apart from a few time changes in the itinerary the ship maintained her overall schedule and did not appear to be affected by the problem with the Azipod which I understand can only be rectified when the ship is in dry dock for her re-fit in November.