ACME DNS renewals don't work

Twice now when a renewal has come due the "certificate.renew_certs" task has errored out. The first time was right when you were fixing the whole ACME form in general, so I figured I'd try and delete the cert and try again, but that hasn't fixed anything:

Status: FAILED
Error: [EINVAL] acme_create.dns_mapping: Please provide DNS authenticator id for DNS:xxxx.xxxx.net

Much of the ACME stuff doesn't make sense. For example, you can create an ACME cert from a CSR, but then you can never see your ACME configuration again. And the UI offers "Create ACME certificate" from a cert itself, not just from a CSR? So weird.