I just checked the various Marriott account web sites. I was PP in 2017, and had similar patterns as last year so would expect to be PP in 2018 (but who knows).
As of just now:
iOS App thinks I'm still PP, and shows 2018 nights-to-date.
Regular web site thinks I'm still PP, and shows end-of-2017 nights earned.
Mobile web site (in chrome on iOS) thinks I'm regular Platinum, and shows 2018 nights-to-date.
Is anyone who's been "demoted" seeing it anywhere but on the mobile (non-app) site? Are ANY PP's seeing their correct status on the mobile site? Of not, I strongly suspect this is just a glitch with the mobile site not knowing about the existence / being able to display PP. In any event, since status is good to the end of February, any demotions are clearly premature.
Unfortunately, there is no single source of data on many internet apps. Seems they each retrieve data and store in a "pre-processed" format for their own quick use. Until all the sweeps are done, the month of January is a scramble to determine the true state of your account. And that's not to mention the random adjustments that may be granted (i.e. gifted status) along the way. So, unless you have a critical event coming up, sit back and see how it all plays out.