The claim was the problem, I don't recall if it was deemed a bug or BAD.
This might be it. As an island it wouldn't trigger colonialism CB, despite being in the middle of my whole island chain with adjacent islands, so only way I had to attack it.
It might also be because my capital was moved to a province in Chesapeake. All the colonies in the Caribbean are functioning as 'same continent'.
In pursuit of sealing off Peru I had England intrude with a colony next to mine, so via colonialism I seized that and the next one they plopped down mid-war. Both of those had the proper 'colony' cost to core afterwards, but they're also definitely not the same continent.. I should have claimed the first one, I suppose, to test if that interfered