Seems to be a new-ish bug. I cancelled a reward ticket and transferred some amex MR points over yesterday, and had three different balances - one in my Aeroplan dashboard on the website, one when I was actually on the booking page, and one on the app. Took about an hour or so for it to finally let me book through the app, although it didn't let me use a travel voucher as a payment method. Typically I've had my balances update more or less instantly. The activity page was correct on both the app and the website throughout, it just didn't seem to be updating somewhere on the backend.