ElasticSearch Fielddata error on Rails 4 app using Chewy gem on one environment but not the other

Question

We have a Rails 4 app running on two similar environments, staging and production.

Lately, this error started appearing on local development environments and the staging environment, but is not happening on production.

Elasticsearch::Transport::Transport::Errors::BadRequest: [400] {
  "error": {
    "root_cause":[{ "type": "illegal_argument_exception",
      "reason":"Fielddata is disabled on text fields by default. 
        Set fielddata=true on [updated_at] 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."}],
      "type":"search_phase_execution_exception",
      "reason":"all shards failed",
      "phase":"query",
      "grouped":true,
      "failed_shards":[{"shard":0,
      "index":"users",
      "node":"xxxxxxxxxxxxxxxxxxxxxxxx",
      "reason":{"type":"illegal_argument_exception",
        "reason":"Fielddata is disabled on text fields by default. 
          Set fielddata=true on [updated_at] 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."}
    }]
  },
  "status":400
}

I know that the ElasticSearch documentation explains how to solve this error. However, I would like to know what could be triggering the error on those environments, given that the ES configuration and queries used are identical in staging and production.