If this was true, you wouldn't be telling us because it would get removed
Do you mean the post would get removed, or the my Expansion Pass? Other than posting those images, I don't know how to prove to you that it is true. You just have to take my word for it, or I see the screenshots.
The expansion pass
That may just have happened. Signing into my Xbox account on a browser shows the buy option and lets me go all the way to the confirm purchase screen. I linked in a picture of it (cut the top of the browser off because I was Facebook chatting with a friend and didn't want his name in the picture) I'm going to hop back on my Xbox and see if it is still there.