[BUG] "Bad MAC" Error When Receiving Private Message

[vllre]

Describe the bug
When receiving a private message, a Bad MAC error occurs and the message cannot be decrypted.
The issue happens consistently across multiple attempts, even after resetting the session.

Error Logs:

Failed to decrypt message with any known session...
Session error: Error: Bad MAC
    at Object.verifyMAC (/root/wa/node_modules/libsignal/src/crypto.js:87:15)
    at SessionCipher.doDecryptWhisperMessage (/root/wa/node_modules/libsignal/src/session_cipher.js:250:16)
    at async SessionCipher.decryptWithSessions (/root/wa/node_modules/libsignal/src/session_cipher.js:147:29)
    at async 6957863858248.0 [as awaitable] (/root/wa/node_modules/libsignal/src/session_cipher.js:171:28)
    at async _asyncQueueExecutor (/root/wa/node_modules/libsignal/src/queue_job.js:20:29)
Closing open session in favor of incoming prekey bundle

Session Details (Closed Sessions)

SessionEntry {
  _chains: {
    'Bb1tY0m5e2qpgJLbbts+wRP2dU+kE5MdUQXEA1Cgmhs0': { chainKey: [Object], chainType: 2, messageKeys: {} },
    'BQ90/dMFGWtPZ4tCsQHRBTFfgLSNmZ0U/XQxXgKFYk9r': { chainKey: [Object], chainType: 1, messageKeys: {} }
  },
  registrationId: 1241753327,
  currentRatchet: {
    ephemeralKeyPair: { pubKey: <Buffer ...>, privKey: <Buffer ...> },
    lastRemoteEphemeralKey: <Buffer ...>,
    previousCounter: 0,
    rootKey: <Buffer ...>
  },
  indexInfo: {
    baseKey: <Buffer ...>,
    baseKeyType: 2,
    closed: -1,
    used: 1756892690842,
    created: 1756892690842,
    remoteIdentityKey: <Buffer ...>
  }
}

To Reproduce
Steps to reproduce the behavior:

1. Receive a private message from another user.
2. Let the session attempt to decrypt the incoming message.
3. The Bad MAC error appears in the logs.
4. Reset the session (delete old session state and reinitialize).
5. Try again — the error still occurs.

Expected behavior
Incoming messages should be decrypted successfully without throwing a Bad MAC error.

Environment:

• "@whiskeysockets/baileys": "^6.7.19",

Additional context

• The error often occurs when the local session state is not synchronized with the sender’s prekey bundle.
• Possible cause: the prekey bundle does not match the remote identity key, even after resetting the session.
• Already tried resetting the session, but the error still persists.

[pvictorlv]

#1735 and #1697 aims to fix this problem

[daniel-n-silva]

This looks like the same mechanism — see #2763 for the root cause (session established under one identity form, incoming stanza addressed via the other) and a fix that retries with the pairing WhatsApp already provides on the stanza (sender_pn/sender_lid).