I have the same problem but im sure theres a little glitch making the button change to Play early, coz the game isnt meant to be playable yet according to release times.
I have this problem as well. I left my vpn on by accident.
Could that be the culprit?
I've turned it off and even uninstalled the vpn, the game, uPlay client and so on.
I found a thread where someone said it was their vpn and that uplay dont like vpn's, but mines not even installed anymore.