Firebase Messaging throws exception and doesn't get back until server restart

I have a system built with spring boot, java 8 and hosted on google cloud using compute engine.
My server app is wildfly 21.0.1.Final.
I am using firebase messaging 9.1.1 to deliver notifications to the application users.
The service is working fine most of the time, however, I get this error from time to time.

` com.google.firebase.messaging.FirebaseMessagingException: Failed to establish a connection: Error getting access token for service account: IP_OF_PROXY_HOST_GOES_HERE, iss: firebase-adminsdk-project@projectname.iam.gserviceaccount.com`

As a workaround, I do a full server (wildfly) restart to get the service back.

In my pom file, I have:

com.google.firebase
firebase-admin
9.1.1

I have searched for similar issues and checked:
1- The system clock is synchronized
2- Firewall access to firebase
3- The service works well and the issue happens randomly from time to time.
4- I can not reproduce since I don't know the cause.

Note: I don't use any other firebase service in this product.

Does anyone know what is happening and how to overcome this issue?

Start with the pom.xml dependency on firebase-admin 9.1.1 and trace the FirebaseMessagingException path for service-account access-token failures. Gather logs around the intermittent failure and compare behavior before and after a WildFly restart; done means identifying a reproducible cause and documenting a reliable fix or confirming an SDK issue.

Written by the indexing model from the issue text.