Heh, interestingly, the actual problem is Deepnesse and Wolfmere shouldn't be connected together, you are meant to go through Hollow Isle to get to Deepnesse, so when Deepnesse tries to "talk" to Wolfmere when it detects inbound migrants the game gets confused and crashes. (In short, Wolfmere is connected to Deepnesse but Deepnesse isn't connected to Wolfmere, so Deepnesse freaks out trying to get data coming from an invalid/nonexistant location)
This is an easy fix on my end, as I need to just remove Deepnesse from Wolfmere's connection list. Problem is the fix won't help you, even next patch, because Deepnesse is already expecting migrants from Wolfmere.
So what I did was made you a custom copy of Deepnesse you can drop in your maps folder, it'll connect the maps together properly, and stop the crash. Just download this zip, and drop it in Rise to Ruins/maps/WorldMaps and overwrite the old Deepnesse.zip, when you restart everything should work fine. I'd suggest not sending anymore migrants from Wolfmere though, as come next patch the patcher will update both maps and disconnect them. So if you still have migrants en route it'll cause the same problem again.