You seem to be having some "fogging" issues with 2 radically different types of photopaper now. I wonder, even though your darkroom is "dark", if you have some sort of radiation issue at work here? Do you think you have some X-ray equipment near to where you work? Or, some radioactive material around that you may not be aware of? Near where you store your paper?
Certain types of toners (for toning prints) can give off fumes that can fog unexposed paper, also.
This is of course speculation, but it wouldn't be completely out-of-line to suggest that you borrow a geiger-counter and measure your background radiation. This would be for your own personal long-term health, as well as the safety of your photo papers.