The region might be splintered due to it being a bay area and almost entirely surrounded by coast. Here's another screenshot of an older area which I had explored almost exclusively by ship before the update. It's probably apparent from the map that it would be impossible to travel that exact same route by boat now. So I think that the jagged islands is just the coastline for mistlands, and when it occurs in "tight" shapes like bay or maybe medium-sized island, it turns out like that.

https://steamcommunity.com/sharedfiles/filedetails/?id=2901550048