Mixpanel Not Recognizing Property Fields in Event Reports

We are pushing through a property as a List of Objects like so. However, in the reports, Mixpanel doesn't recognise it and I am getting not set for the field key, even though it has a value. Any ideas?

{
  "event": "search",
  "properties": {
    "Filters": [
      {
        "field": "Title",
        "operator": "contains",
        "value": "kos"
      }
    ]
  }
}