Unreliable 401 errors with GCM services

问题:

I implemented a GCM push notification service that runs on my computer (at least during development).

To do that, I basically format and send requests to https://android.googleapis.com/gcm/send.

For authentication, I obviously used a server key I generated on the Google Developers console.

I tested it and it works perfectly (the devices receive the push notification, and it's actually damn fast).

I send those push notifications several times in the day, but yesterday I faced a situation were the request sending returned a 401 (which stands for authentication required). My request was exactly the same as usual. I retried 4 times with the same result then suddenly, it worked again and returned a 200.

I'm at loss trying to understand why this happens. According to this documentation, 401 is only supposed to happen if:

• Authorization header missing or with invalid syntax.
• Invalid project number sent as key.
• Key valid but with GCM service disabled.
• Request originated from a server not whitelisted in the Server Key IPs.

None of these conditions have changed between the different calls.

Is there some kind of threshold or quota that might explain this ? Or is there a guideline regarding what to do when this happens ?