PFUser.becomeInBackground never returns in watchOS2

Question

In watchOS2 I am getting the sessionToken from the iOS app with WCSession. That works great but when I try to call become in background it never returns. The console logs 1 and 2 but never makes it to print("3"). Any reason becomeInBackground wouldn't respond at all? Or is there a completely different way I should be going about this?

The sessionToken is coming from user.sessionToken in iOS.

print("1")
if let sessionToken = reply["sessionToken"] as? String {
    print("2")
    PFUser.becomeInBackground(sessionToken, block: { (user, error) in
        print("3")
        if let user = user as? User where error == nil {
           print("success")
        } else {
           print(error)
        }
    })
}