Update: I found the work around.
The issue is (what a surprise) IT related. Even when logging in into Marriott/spg (the site you will be redirected to) Marriott IT will still recognize you as MR member and will auto log you in into your MR account.
So make sure to clear known user, put in your SPG account number and then log in. This will generate your new SPG account number and will log you in into the SPG side.
Unfortunately my account shows as Platinum, not PP. Wait and see.