DB durability failures could cause key reuse
If an outgoing stream number is used and the database fails to store the updated stream counter durably, the stream number could be reused after restarting the app. That would mean the same key would be reused with the same IV, which would be very serious - the XOR of two GCM ciphertexts created with the same key and IV equals the XOR of the plaintexts, making the plaintexts guessable.
If this document is right, databases generally can't guarantee durability, even if they claim to:
We should use a fresh random IV for each stream to avoid reusing the same (key, IV) combination even if a stream number is reused.