The desc explicitly states this is the count of IPsec decompression errors, failures during the decompression step. A nonzero value here means data arrived correctly decrypted but then failed to decompress, showing up as corrupted or dropped application data over that specific tunnel even though the encryption and authentication layers reported success, a distinct failure mode from any of the SA-level errors elsewhere in this MIB. e.g. cpvIpsecDecomprErr incrementing after a peer's IPComp implementation sent a malformed compressed payload, causing this gateway to discard otherwise-valid decrypted packets.