Hey! I have the same or similar issue. I thought mine got messed up when I modified my last night to a AKV stay. I was fine until I made that change this week. I cannot make FP changes, I am grayed out on the app and non existent on the online site. The only days I can modify are days after my check-out date.
I called this afternoon. They could not figure it out but said they would try. I think they are working on it because I have gotten a couple of emails on the past hour asking me to join my friends on their MDE plans (they are using my husbands email address).
I check-in in 3 days! On Friday so crossing my fingers. They said the resort could fix it once I arrived if they couldn't.