Push notifications dilemma!!

I hope someone can help us with this:

Push notification doesn't work well. It sometimes send notifications, but other times, the push notifications all stuck in the Queue. (we tried this with both RC2 and RC3 versions) and all the same. Website and email notifications work well, but not the Push.

Cron job is tested and works well. All keys/APIs re checked OK. All setting or good.

Not sure what the issue, is!