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Unfortunately, the fix has an unintended side effect. Although the receiving end of the transfer has been able to detect to and discard messages with duplicate ACK_WINDOW packet IDs since its delivery in 5.2.0.1, the discarded messages aren’t acknowledged back to the sender until version 6.3.0.4.
The sending party is unable to know whether the packet it sends will be treated by the receiver as a duplicate, so it expects that every packet will be acknowledged. If this acknowledgement isn’t received, the sender behaves as though another network fault has occurred and will enter NFT recovery.
When the recovery completes, the sender will re-send the packet, the receiver will discard it, and the sender will be left waiting for another acknowledgement. This is treated again like a network fault, and the cycle repeats, essentially creating an NFT recovery loop where no additional data is transferred.
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