[solved] Kibana Monitoring [illegal_argument_exception]

I'm on my Lab to update from 6.6.1 to 7.2
After all work done, I had on the tab Monitoring this error on the lower right corner of the browser:

Monitoring Request Error
Fielddata is disabled on text fields by default. Set fielddata=true on [event.dataset] in order to load fielddata in memory by uninverting the inverted index.Note that this can however use significant memory. Alternatively use a keyword field instead.: Check the Elasticsearch Monitoring cluster network connection or the load level of the nodes.
HTTP 503

I've then done a search for this [event.dataset] under Management->Kibana, index patterns.
On each pattern I've entered this event.dataset until I've found it. In my case it was in filebeat-
In Management -> Elasticsearch, Index Management I've entered filebeat- and saw (for my luck) only one index.
In the Dev tools:

PUT filebeat-[something]/_mapping
  "properties": {
    "event.dataset": { 
      "type":     "text",
      "fielddata": true

This did the right stuff, to remove [illegal_argument_exception]

Hopefully there are someone out there, which could help my finding.