buffer flush took longer time than slow_flush_log_threshold

Question

I am getting following Error in kibana-
buffer flush took longer time than slow_flush_log_threshold.
Don't know how to solve this.
does anyone know how to solve this ?

Things done so far-

1. ES data nodes were filled 95%, so freed up some space, now at 70%
2. cluster health was yellow, after freeing up space turned green.

However, still not able to get data in Kibana.

Answer 1

in kibana dev tools, do this-

PUT /_all/_settings
{
  "index" : {
      "blocks" : {
          "read_only_allow_delete" : "false"
        }
  }
}