Maybe if your system has trouble contacting the Google PUSH servers, usually might happen if you have a strict firewall which sometimes decides to block traffic while other times it lets it pass through.
Thanks for sending us the logs required to look into the issue
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After further investigation, we concluded that this most probably is a connection issue
When trying to send a push message to https://fcm.googleapis.com/fcm/send, the server closes the connection, or perhaps something in the middle (bad internet connection).
In our logs, we got an exception: SocketException (104): Connection reset by peer which shows this.