aws_route53_health_check error when switching back to recommended regions

debug.log

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  ~ module.cluster.module.route53.aws_route53_health_check.status
      regions.#:          "3" => "0"
      regions.1441947086: "us-west-2" => ""
      regions.2003110180: "us-east-1" => ""
      regions.3439004788: "us-west-1" => ""


Plan: 0 to add, 1 to change, 0 to destroy.

Do you want to perform these actions?
      Terraform will perform the actions described above.
      Only 'yes' will be accepted to approve.

      Enter a value: yes


module.cluster.module.route53.aws_route53_health_check.status: Modifying... (ID: 54d24e9b-823c-4877-aa20-390ed11ca396)
  regions.#:          "3" => "0"
  regions.1441947086: "us-west-2" => ""
  regions.2003110180: "us-east-1" => ""
  regions.3439004788: "us-west-1" => ""

Error: Error applying plan:

1 error(s) occurred:

* module.cluster.module.route53.aws_route53_health_check.status: 1 error(s) occurred:

* aws_route53_health_check.status: InvalidParameter: 1 validation error(s) found.
- minimum field size of 3, UpdateHealthCheckInput.Regions.


Terraform does not automatically rollback in the face of errors.
Instead, your Terraform state file has been partially updated with
any resources that successfully completed. Please address the error
above and apply again to incrementally change your infrastructure

I'm omitting DEBUG output because the issue is very easy to reproduce.