I had the same problems before, that`s why I still working on DS3a until I finish the project.
All my old scenes were built on DS3, but seems that just complexes meshes like V4 and M4 don`t work properly.
BUT did one thing that made DS4 correct the V4 meshes once, and then I could open my scene:
1. Open a new project.
2. Load the main model (v4, m4, dragon or any other complex model that you have problem loading)
3. Load ALL the morphs for that model. On my case it were a V4 with all my 10 morphs (muscle,++, steph, aiko, old, distinctive, g4, shefreak, nbm, ngt etc)
4. Load the custom morph like the character face/body/skin (example,
5. Place the custom inj or fix if you were using any.
6. Save the project anywhere.
This save may create some files on your content/data folder that will allow you to open your scene again.
Another thing, I suggest you to create new base models to use on DS4.5, maybe it is the only chance to go from one to another without loosing everything, and always keep a copy of the older project.
I bought a lot of genesis stuff, if my characters become stable there I will begin the migration, slowly, really slowly.