No push sent to Android devices

Hi.

Our SNS service stopped sending out push messages within the last couple days. There have been no changes in our service and when I use the "Publish message" feature to test an endpoint, it just says the message is sent but never shows up (we've tried several of our own devices). Doing the same for an iOS device the message is sent and delivered instantly.

I have no idea what is going on, we've been using SNS for a long time. Anyone has any idea?