Ingest pipe line csv parser with multiline message failing

I am using a csv processor and \t as the separator ingest pipeline to push logs from filebeat. This works great but fails when the message (logmessage) portion has a new line character. I added the following to the filebeat.yml to deal with multiline but hasn't helped. Loglines start with a TS like 2020-12-29T08:25:01.971....

Any help would be great?

filebeat.yml
multiline.type: pattern
multiline.pattern: '^20'
multiline.match: after
multiline.negate: true

pipeline def

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  "pipeline_tab" : {
    "description" : "tab pattern",
    "processors" : [
      {
        "csv" : {
          "field" : "message",
          "target_fields" : [
            "timestamp",
            "relativeTime",
            "thread",
            "processName",
            "sourceName",
            "logType",
            "logMessage"
          ],
          "separator" : "\t"
        }
      }
    ]
  }