The issue is with the engine and has been known and discussed here for a while. There was a posting earlier saying they were starting repairs this week so we were still hopeful that it would be resolved by the time we sailed.
For the August 29th sailing they said this:
Due to speed limitations caused by a technical issue with one of the ship’s engines, instead of visiting Endicott Arm & Dawes Glacier, we’ll visit Juneau on Friday, with a little extra time to explore this beautiful destination.
For September 5th, it was this.
Due to speed limitations caused by a technical issue with one of the ship’s engines, we’ve replaced our visit to Icy Strait Point, Alaska with Ketchikan, Alaska. Additionally, instead of visiting Endicott Arm & Dawes Glacier on Friday, we’ll have a full day in Juneau, Alaska.