Heatmap charts in monitoring dashboard is broken

Summary

Heatmap charts in the monitoring dashboard are broken. I created a chart with the example provided in the docs https://docs.gitlab.com/ee/user/project/integrations/prometheus.html#heatmaps in the all_chart_type dashboard in the monitor-sandbox project. The page loads but the heatmap doesn't show up.

I used the following config from the docs

dashboard: 'Dashboard Title'
panel_groups:
  - group: 'Group Title'
    panels:
      - title: "Heatmap"
        type: "heatmap"
        metrics:
        - id: 10
          query: 'sum(rate(nginx_upstream_responses_total{upstream=~"%{kube_namespace}-%{ci_environment_slug}-.*"}[60m])) by (status_code)'
          unit: req/sec
          label: "Status code"

Sample project

https://gitlab.com/gitlab-org/monitor/monitor-sandbox/-/environments/711946/metrics?dashboard=.gitlab%2Fdashboards%2Fall_chart_types.yml

Screenshot