Invalid index in dynamic block

I have the following module:

module "nlb_mqtt_public" {
  source             = "..." # module source
  ... # other fields

  vpc_id             = module.vpc_base.vpc_id

  listen_map = {
    "8884"  = "8883"
    "50858" = "8883"
    "60858" = "60858" 
    "60859" = "60859" 
    # "28883" = "28883"
    "443" = "28883"
  }

  healthcheck_map = {
    "8883" = {
      interval = "10"
      path     = "/heartbeat"
      port     = "9090"
      protocol = "HTTP"
    }
  }
}

And in the external module that I am referencing in the source, it fails in this part:

resource "aws_lb_target_group" "this-health" {
  count             = length(var.healthcheck_map) >= 1 ? length(distinct(values(var.listen_map))) : 0
  name              = "${random_string.target.keepers.name}-port-${element(values(var.listen_map), count.index)}-${random_string.target.result}"
  protocol          = "TCP"
  port              = element(distinct(values(var.listen_map)), count.index)
  vpc_id            = var.vpc_id
  proxy_protocol_v2 = random_string.target.keepers.enable_proxy_protocol_v2

  dynamic "health_check" {
    for_each = [var.healthcheck_map[element(distinct(values(var.listen_map)), count.index)]] # it fails here
    content {
      enabled             = lookup(health_check.value, "enabled", null)
      healthy_threshold   = lookup(health_check.value, "healthy_threshold", null)
      interval            = lookup(health_check.value, "interval", null)
      matcher             = lookup(health_check.value, "matcher", null)
      path                = lookup(health_check.value, "path", null)
      port                = lookup(health_check.value, "port", null)
      protocol            = lookup(health_check.value, "protocol", null)
      timeout             = lookup(health_check.value, "timeout", null)
      unhealthy_threshold = lookup(health_check.value, "unhealthy_threshold", null)
    }
  }

  lifecycle {
    create_before_destroy = true
  }
}

and in this

data "template_file" "healthcheck_port" {
  count    = length(var.healthcheck_map) >= 1 ? length(distinct(values(var.listen_map))) : 0
  template = var.healthcheck_map[element(distinct(values(var.listen_map)), count.index)]["port"]
}

It shows the following error:

Error: Invalid index
  on .terraform/modules/nlb_mqtt_public/main.tf line 51, in resource "aws_lb_target_group" "this-health":
  51:     for_each = [var.healthcheck_map[element(distinct(values(var.listen_map)), count.index)]]
    |----------------
    | count.index is 0
    | var.healthcheck_map is map of map of string with 1 element
    | var.listen_map is map of string with 5 elements
The given key does not identify an element in this collection value.
Error: Invalid index
  on .terraform/modules/nlb_mqtt_public/main.tf line 51, in resource "aws_lb_target_group" "this-health":
  51:     for_each = [var.healthcheck_map[element(distinct(values(var.listen_map)), count.index)]]
    |----------------
    | count.index is 2
    | var.healthcheck_map is map of map of string with 1 element
    | var.listen_map is map of string with 5 elements
The given key does not identify an element in this collection value.
Error: Invalid index
  on .terraform/modules/nlb_mqtt_public/main.tf line 51, in resource "aws_lb_target_group" "this-health":
  51:     for_each = [var.healthcheck_map[element(distinct(values(var.listen_map)), count.index)]]
    |----------------
    | count.index is 3
    | var.healthcheck_map is map of map of string with 1 element
    | var.listen_map is map of string with 5 elements
The given key does not identify an element in this collection value.
Error: Invalid index
  on .terraform/modules/nlb_mqtt_public/main.tf line 150, in data "template_file" "healthcheck_port":
 150:   template = var.healthcheck_map[element(distinct(values(var.listen_map)), count.index)]["port"]
    |----------------
    | count.index is 3
    | var.healthcheck_map is map of map of string with 1 element
    | var.listen_map is map of string with 5 elements
The given key does not identify an element in this collection value.
Error: Invalid index
  on .terraform/modules/nlb_mqtt_public/main.tf line 150, in data "template_file" "healthcheck_port":
 150:   template = var.healthcheck_map[element(distinct(values(var.listen_map)), count.index)]["port"]
    |----------------
    | count.index is 0
    | var.healthcheck_map is map of map of string with 1 element
    | var.listen_map is map of string with 5 elements
The given key does not identify an element in this collection value.
Error: Invalid index
  on .terraform/modules/nlb_mqtt_public/main.tf line 150, in data "template_file" "healthcheck_port":
 150:   template = var.healthcheck_map[element(distinct(values(var.listen_map)), count.index)]["port"]
    |----------------
    | count.index is 2
    | var.healthcheck_map is map of map of string with 1 element
    | var.listen_map is map of string with 5 elements
The given key does not identify an element in this collection value.

I don't understand why. The healthcheck_map variable is defined with the type map(map(string)) and default as {}.

Previously, I had some issues in another tf files, where the error suggested me to use the -target argument, so I thought that it may be the case here too, but it does not work.

values returns values in alphanumerical order, not in the order you have them defined. Thus, the first value returned will be 28883. Subsequently, var.healthcheck_map["28883"] fails, because var.healthcheck_map has only 8883 key, not the required 28883.

Basically, your values in var.listen_map do not match keys in var.healthcheck_map.