Changes applied on every terraform run

Terraform apply always shows this:

  ~ module.es.aws_elasticsearch_domain.es_vpc
      advanced_options.rest.action.multi.allow_explicit_index: "true" => ""
      ebs_options.0.volume_type:                               "" => "gp2"

Module definition:

module "es" {
  source        = "github.com/terraform-community-modules/tf_aws_elasticsearch?ref=v0.8.0"
  domain_prefix = "${var.domain_prefix}"
  domain_name   = "${var.domain_name}"

  vpc_options = {
    security_group_ids = ["${data.terraform_remote_state.region_state.xxx}"]
    subnet_ids         = [
      "${data.terraform_remote_state.region_state.private_subnets.0}",
      "${data.terraform_remote_state.region_state.private_subnets.1}"
    ]
  }
  instance_count        = 12
  instance_type         = "i3.2xlarge.elasticsearch"
  dedicated_master_type = "i3.xlarge.elasticsearch"
  es_zone_awareness     = true
  create_iam_service_linked_role = false
  management_iam_roles  = [
    "arn:aws:iam::999999:role/xxx-xxxx-logs"
  ]
}

Am I missing something?

terraform-community-modules / tf_aws_elasticsearch

Changes applied on every terraform run #24