The Only fix I know, off the top of my head, is to manually go into the content folder and delete the last thing you added and then re-run the build. If it was a blueprint, go into the content folder and delete that blueprint. You should be able to open the file after doing so?
I don’t use alembic files. I have never really had issues with FBX and OBJ. As for manually just adding the file, I have never tried it. With the one file per actor feature…?
Ask away. If I can help, I most certainly will try.
If you do decide to delete the file manually and then restart, It might effect the build when you bake the game. I think, even though it’s erased, the editor will still look for. It might just throw a warning that it cant find the file, but I don’t know for sure.