It seems to crash on adjacencies, according to the logs. No errors reporting, but it gets as far as adjacencies before stopping, which would make sense with a creating paths crash, I guess. I don't see why though, since there should be no extra adjacency needed in adjacencies.txt, just as there isn't for Wessex to the Isle of Wight, or the Isles around Scotland.
Interestingly I decided to try it on the vanilla map in case there was a problem with my new files, and it had exactly the same error. I've checked the bits with vanilla and other mods, they all match up, 8bit for some, 24bit for others.
I drew this map from scratch with some islands around, they work fine. It's just this one I'm adding in now, it's bizarre.
I'll try again tomorrow. I'm probably missing something obvious my tired brain refuses to see

Thanks.