Yeah, hows that going for ya?
I've just shutdown my PC, reopened a blank reason template, opened a dr octorex, redrum, malstrom, nn19.
Been able to browse all my rex files, Refill files and wav samples more or less instantly after doing that workaround. I don't have lots of sub folders, and my samples are not organised like I guess you guys have, i'm lazy! But Reason still took a minute or so to open refills/folders. Not sure how or why the workaround works, but it's done the job for me at least.