I've had this problem too, with large blank gaps in the Project Explorer. I've discovered that the names are really there even though I can't see them. If I get lucky and click on the correct part of the blank space, it takes me to the correct person. But it's a trial-and-error sort of thing and I'm tired of it.
Like David, I'd appreciate any help that someone can give with how to fix this blank Explorer problem.
Linda