DxO Optics Pro 8 problems
It's not a problem with the software you're using as accessing images on externally attached drives is a very normal way of working and therefore if there was a real issue it would affect everyone who works this way.
You've had the same issue with two completely independent applications. What does that tell you?
It tells me your problem is somewhere in your setup or your workflow. If you provide more info maybe someone can help.