I can sign in again with both accounts.

Oddly, the primary page when I sign in with my Rewards account still incorrectly indicates "Platinum Elite" — even though all references to my status elsewhere on the website correctly indicate "Platinum Premier Elite" or "Lifetime Platinum Premier Elite." One would think this would be very easy to fix, given that the website obviously has access to the correct information.

Also, oddly, the primary page when I sign in with my SPG account indicates "Platinum Elite" — even though have never had status higher than Gold with SPG. I linked my accounts in 2016, but I'm holding off on combining them until the system appears to be more stable.