I was able to find a bug that happens when you migrate from 4.7 to 4.8 which completely crashes your blueprint editor preventing it from ever opening again. I have reproduced this in following way:
1)Open a New 4.7 blank project.
2)Create a BlueprintFunctionLibrary
3)Inside of FunctionLibrary, create a new function
4)Create a local variable of HitResult
5)Drag a get reference to blueprint graph
6)One HitResult variable get node you just pulled out, Right click and “Split Struct”
Save project.
7)Create a New 4.8 blank project
8)From your 4.7 project, Migrate your BlueprintFunctionLibrary to your new 4.8 project.
9)Open your 4.8 project and try opening level blueprint.
It crashes engine hardcore. root cause I have it down to is that HitResult Split Struct is not supported when moved to 4.8.