I’m having this same problem too. I have over 300GB of SDX libraries I purchased, they are on an external SSD hooked up to my new computer. I’ve installed SD3 and that’s running fine. I’ve went into SD settings and added the additional library path for my SSD but SD3 still can’t see/find my SDX.
When I go into product manager, it shows they are not installed and giving me the option to download them again. I should not have to download them again. That’s pointless.