When you send a push notification request to the APNs service, you send one for each unique device token. For example, if you want to send a push notification to 100 unique devices, you send 100 requests. Each request has a unique device token.
The error you are receiving indicates that instead of sending a single request to each device token, you are instead sending numerous requests to the same device token. You are sending too many updates to the same token.
[Some suggestions]
If you have a way to check your code, verify that your device tokens being sent in the requests are unique.
Make sure your code does not have a repetition loop in there whch might be sending multiple requests to each device.