FirebaseInstallations migration from FirebaseInstanceId generates new device ID after BOM upgrade (24.6.0 → 34.5.0)

[advantagepsteam-collab]

Component: firebase-installations (Android)
Firebase BOM: migrated from 24.6.0 → 34.5.0 during an application update
Platform: Android
Reproducible in internal testing or UAT: No (see details below)

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Summary

After upgrading from Firebase BOM 24.6.0 to 34.5.0, the deprecated FirebaseInstanceId API was replaced with FirebaseInstallations as required by the migration. These two APIs produce identifiers of a different format and length:

API	Example ID	Length	Format
FirebaseInstanceId (old)	cqQdF_tJux8	~11 chars	Instance ID
FirebaseInstallations (new)	elKPQ-9JTFyHlhdRQmuTDG	~22 chars	Firebase Installation ID (FID)

By our testing and understanding, the Firebase SDK includes a migration path intended to preserve the existing Instance ID.
However, in production this migration fails silently for a significant subset of users, generating a new 22-character FID instead of returning the preserved 11-character Instance ID.

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Impact

Production log analysis from a 15-hour window covering 333 unique Android users

• 209 users (62.8%) — migration succeeded, existing Instance ID preserved
• 124 users (37.2%) — migration failed, new FID generated, device ID no longer matches server-stored value

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Key Observations from Production Logs

1. The different behavior is not tied to device brand, Android version, or any identifiable client-side variable. Identical device models show both outcomes.

2. Format difference is the only discriminating signal. Failed attempts present a 22-character FID. Successful attempts present the original 11-character Instance ID. This format difference is the sole consistent distinguishing factor between the two groups.

3. Not reproducible in internal testing. Testing across more than a dozen devices of varying brands and Android versions did not reproduce the failure. The Firebase migration logic that determines whether a cached Instance ID is available is not publicly documented.

4. User base is located in Australia.

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Questions for the Firebase Team

1. What are the exact conditions under which FirebaseInstallations will not preserve an existing FirebaseInstanceId during migration?
2. Is there a known issue with the migration path in specific BOM version ranges between 24.6.0 and 34.5.0?

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Environment

• Firebase BOM (before): 24.6.0 — using firebase-iid / FirebaseInstanceId
• Firebase BOM (after): 34.5.0 — using firebase-installations / FirebaseInstallations