I was having the same issue but I do not use good sky. It happened to me because I had an event that was bound to another event but I used a re-route node in UE4 and disconnected the event but left it connected to the re-route node. This caused a crash throughout my project because that specific blueprint was a base blueprint used almost everywhere. If anyone runs into the issue and has questions feel free to ask. To fix it just remove the re-route node or make sure all re-route node are connected to something before migrating then just migrate the project again and it should work!
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