I encounter the same issue here: https://stackoverflow.com/questions/59795325/approved-kubernetes-csr-but-certificate-not-shown-in-status

No certificate was issued in .status.certificate though the status is "Approved". This issue only occurs when I use certificates.k8s.io/v1 but certificate is issued when I use certificates.k8s.io/v1beta1. I have already followed adding /O=system:nodes/CN=system:node:mypod.svc but still no certificate is issued. Here is the sample of my CSR.

apiVersion: certificates.k8s.io/v1
kind: CertificateSigningRequest
metadata:
  name: mypod.default
spec:
  groups:
  - system:authenticated
  - system:nodes
  request: $(cat server.csr | base64 | tr -d '\n')
  signerName: kubernetes.io/kubelet-serving
  usages:
  - digital signature
  - key encipherment
  - server auth
EOF