Our server sends one push notification to a device. The notification arrives and the user does not delete the message. Now the same message arrives at the device in a one minute cycle. We checked and our server only sends one message. Does the GCM resend notifications?
We found it. It's a setting on the Samsung Galaxy:
Settings > Accessibility > Notification Reminder > ON
It's possible to set the interval. Ours happened to be 1 minute.