A lot of the performance team Grafana dashboards aren't working correctly because of the dashboards gets 502:s for queries in Graphite. I'm not sure when this started to happen, but I know it has been like this for at least before the latest Grafana update. Probably a couple of months at least.
This happens on large dashboards like https://grafana.wikimedia.org/d/000000491/webpagereplay-desktop-alerts but sometimes on smaller ones like https://grafana.wikimedia.org/d/000000210/webpagetest .
It can be that a panel doesn't work, and sometimes one of the queries in the panel. Refreshing the dashboard makes other dashboards fail. It looks like this in devtools: