PANOS filebeat doesn't parse VPN logs

as per title, the following is an example of logs received and parsed by panos beat.
Notice that event.original has been preserved but it's content related to the actual message is lost after parsing.

{
  "_index": ".ds-filebeat-8.3.2-2022.07.12-000001",
  "_id": "g-ZHIIIBSFUr2RK98qZE",
  "_version": 1,
  "_score": 0,
  "_source": {
    "agent": {
      "name": "panw-beat-beat-filebeat-sn7wn",
      "id": "00469ffe-3751-4cbd-8d9c-a0ea3f4dfb2d",
      "ephemeral_id": "7721b1ae-2d39-4b6a-b2bd-3f2c4878591f",
      "type": "filebeat",
      "version": "8.3.2"
    },
    "log": {
      "source": {
        "address": "192.168.195.62:57745"
      }
    },
    "syslog": {
      "priority": 14,
      "facility": 1,
      "severity_label": "Informational",
      "facility_label": "user-level"
    },
    "fileset": {
      "name": "panos"
    },
    "panw": {
      "panos": {
        "sub_type": "vpn",
        "type": "SYSTEM"
      }
    },
    "tags": [
      "pan-os",
      "forwarded",
      "_geoip_database_unavailable_GeoLite2-ASN.mmdb",
      "_geoip_database_unavailable_GeoLite2-ASN.mmdb"
    ],
    "input": {
      "type": "syslog"
    },
    "observer": {
      "product": "PAN-OS",
      "vendor": "Palo Alto Networks",
      "serial_number": "001701001659",
      "type": "firewall"
    },
    "hostname": "panorama-02.schibsted-it.no",
    "@timestamp": "2022-07-21T12:22:38.000Z",
    "ecs": {
      "version": "1.12.0"
    },
    "service": {
      "type": "panw"
    },
    "event": {
      "severity": 6,
      "ingested": "2022-07-21T10:22:42.243427234Z",
      "original": "1,2022/07/21 12:22:41,001701001659,SYSTEM,vpn,0,2022/07/21 12:22:38,,ikev2-nego-child-start,ikeGW-SR22189880,0,0,general,informational,\"IKEv2 child SA negotiation is started as responder, rekey. Initiated SA: 152.90.201.42[500]-13.49.81.211[500] message id:0x0000004A.\",24104144,0x8000000000000000,0,0,0,0,,vpn-gw-02",
      "timezone": "+00:00",
      "created": "2022-07-21T12:22:41.000Z",
      "module": "panw",
      "dataset": "panw.panos",
      "outcome": "success"
    }
  },
  "fields": {
    "syslog.facility": [
      1
    ],
    "service.type": [
      "panw"
    ],
    "observer.vendor": [
      "Palo Alto Networks"
    ],
    "hostname": [
      "panorama-02.xxxxxxxxxx.no"
    ],
    "agent.type": [
      "filebeat"
    ],
    "event.module": [
      "panw"
    ],
    "panw.panos.sub_type": [
      "vpn"
    ],
    "panw.panos.type": [
      "SYSTEM"
    ],
    "observer.product": [
      "PAN-OS"
    ],
    "agent.name": [
      "panw-beat-beat-filebeat-sn7wn"
    ],
    "event.timezone": [
      "+00:00"
    ],
    "event.outcome": [
      "success"
    ],
    "event.severity": [
      6
    ],
    "event.original": [
      "1,2022/07/21 12:22:41,001701001659,SYSTEM,vpn,0,2022/07/21 12:22:38,,ikev2-nego-child-start,ikeGW-SR22189880,0,0,general,informational,\"IKEv2 child SA negotiation is started as responder, rekey. Initiated SA: 152.90.201.42[500]-13.49.81.211[500] message id:0x0000004A.\",24104144,0x8000000000000000,0,0,0,0,,vpn-gw-02"
    ],
    "syslog.priority": [
      14
    ],
    "fileset.name": [
      "panos"
    ],
    "input.type": [
      "syslog"
    ],
    "agent.hostname": [
      "panw-beat-beat-filebeat-sn7wn"
    ],
    "tags": [
      "pan-os",
      "forwarded",
      "_geoip_database_unavailable_GeoLite2-ASN.mmdb",
      "_geoip_database_unavailable_GeoLite2-ASN.mmdb"
    ],
    "observer.serial_number": [
      "001701001659"
    ],
    "event.ingested": [
      "2022-07-21T10:22:42.243Z"
    ],
    "syslog.severity_label": [
      "Informational"
    ],
    "@timestamp": [
      "2022-07-21T12:22:38.000Z"
    ],
    "agent.id": [
      "00469ffe-3751-4cbd-8d9c-a0ea3f4dfb2d"
    ],
    "ecs.version": [
      "1.12.0"
    ],
    "observer.type": [
      "firewall"
    ],
    "log.source.address": [
      "192.168.195.62:57745"
    ],
    "event.created": [
      "2022-07-21T12:22:41.000Z"
    ],
    "syslog.facility_label": [
      "user-level"
    ],
    "agent.ephemeral_id": [
      "7721b1ae-2d39-4b6a-b2bd-3f2c4878591f"
    ],
    "agent.version": [
      "8.3.2"
    ],
    "event.dataset": [
      "panw.panos"
    ]
  }
}