ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR: duplicate key value violates unique constraint "index_issues_on_proj...

https://sentry.gitlab.net/gitlab/gitlabcom/issues/1061236/

PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_issues_on_project_id_and_iid"
DETAIL:  Key (project_id, iid)=(14682755, 83) already exists.

  active_record/connection_adapters/postgresql_adapter.rb:611:in `async_exec_params'
    @connection.exec_params(sql, type_casted_binds)
  active_record/connection_adapters/postgresql_adapter.rb:611:in `block (2 levels) in exec_no_cache'
    @connection.exec_params(sql, type_casted_binds)
  active_support/dependencies/interlock.rb:48:in `block in permit_concurrent_loads'
    yield
  active_support/concurrency/share_lock.rb:187:in `yield_shares'
    yield
  active_support/dependencies/interlock.rb:47:in `permit_concurrent_loads'
    @lock.yield_shares(compatible: [:load]) do
...
(198 additional frame(s) were not displayed)

ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_issues_on_project_id_and_iid"
DETAIL:  Key (project_id, iid)=(14682755, 83) already exists.
: INSERT INTO "issues" ("title", "author_id", "project_id", "created_at", "updated_at", "description", "state", "iid", "title_html", "description_html", "relative_position", "cached_markdown_version", "lock_version", "time_estimate") VALUES ('testing', 4744999, 14682755, '2019-11-14 06:53:19.542278', '2019-11-14 06:53:19.542278', '', 'opened', 83, 'testing', '', 1073783823, 1179652, 0, 0) RETURNING "id"

ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_issues_on_project_id_and_iid"
DETAIL:  Key (project_id, iid)=(14682755, 83) already exists.
: INSERT INTO "issues" ("title", "author_id", "project_id", "created_at", "updated_at", "description", "state", "iid", "title_html", "description_html", "relative_position", "cached_markdown_version", "lock_version", "time_estimate") VALUES ('testing', 4744999, 14682755, '2019-11-14 06:53:19.542278', '2019-11-14 06:53:19.542278', '', 'opened', 83, 'testing', '', 1073783823, 1179652, 0, 0) RETURNING "id"

ZD: https://gitlab.zendesk.com/agent/tickets/138625

500 error is observed on issue creation.