Same thing happened to me
I had 24 stays as of mid-December. Did one more stay, thought I had made Plat, and now SPG is telling me that I had 22 stays instead of 25. I have been Plat for several years so I hope SPG will do right by me and grant me a platinum exception. I relied on their information, thinking I had enough stays. My guess is that their website was erroneously counting my points stays as qualifying stays, because if you add those back in, the math works.