Helm Chart - can't download on non-local k3s

After a fresh install of Rancher via Docker, in Cluster Explorer I add the helm repository, it is fine.
Several days later I find it is in “downloading” state, and red. I click into it and see:

Get "https://charts.bitnami.com/bitnami/index.yaml": dial tcp: lookup charts.bitnami.com on 10.43.0.10:53: server misbehaving

When I switch to the default local k3s, I can add it no problem.
This has happened more than once, and after re-installing Rancher it goes away for a bit, but it’s been a week now and my project can’t download helm charts.

The solution was coredns, updating manually:
https://crt.the-mori.com/2020-03-18-coredns-connection-timeout-external-domain-name