The desc explicitly states this is the count of decryption errors — failures encountered while trying to decrypt inbound packets. A rising value here means inbound VPN packets are arriving but failing to decrypt, the mirror-image symptom of cpvErrOut, and typically points at a key mismatch between the peers rather than at a network problem. e.g. cpvErrIn climbing right after a peer rekeyed its side of the tunnel while this gateway kept using stale key material, causing every subsequent inbound packet to fail decryption until the next successful rekey.