Exception missing in response for failed ones.

When large number of failures, no exception details present in response but only error count. The count of exceptions in response do not match failed count. That means for some failures exception objects are missing.

Documentation https://firebase.google.com/docs/reference/admin/error-handling says "Every API error is guaranteed to contain an error code and an error message" which is not the case here.

Notification is send to registration tokens of almost 2.3 million. Almost 2.2 million are success. For around 88k no exception present in response. I use firebase admin SDK 9.1.1. The method used is sendMulticast().

Sample usage:
BatchResponse response = fcmMessaging.sendMulticast(multiCastMessage, dryRun);

Start at the sendMulticast() entry point and inspect how its BatchResponse represents failed registration tokens, using the reported Firebase Admin SDK 9.1.1 behavior and the linked error-handling documentation as context. Reproduce the large-batch case if possible, then verify that every failed token has an exception and that exception and failure counts match.

Written by the indexing model from the issue text.