I still have issues with this. A few days ago I finally showed up as Plat Premier in the Marriott app and website. However, that status has not transferred back to SPG. I had three reservations at the time of the 'upgrade' to Plat Premier with SPG and I've just used two of them this weekend. Both of them showed me as Platinum only.
I'm sure Marriott isn't really interested in doing another data sweep "backwards" from Marriott to SPG but I think they need to. Otherwise, I have no way of having any SPG property see me as Platinum Premier right now.
-RM