I think it's just me, but they haven't explained why.

They told me I probably got logged out, to hit the gear icon (yes, in the app) and scroll down to the card and try to log back in.  That is, re-associate the card to the app.

Well, I did that but it just gives the bouncing 'b' logo then an "Oops..." page.

Today the card is completely missing so I can't even re-add it.