Vault: login unauthorized due to: Post apis/": dial tcp: i/o timeout

I’m using vault in k8s cluster as external one, when I hit the vault cluster endpoint using k8s auth sometimes its providing auth token but sometimes throwing below error with permission denied:
curl --request POST --data ‘{“jwt”: "’"$SA_JWT_TOKEN"’", “role”: “vault-auth”}’ | jq


  "errors": [
    "permission denied"

When I check the logs in vault server logs:

[ERROR] auth.kubernetes.auth_kubernetes_XXXXXX: login unauthorized due to: Post "": dial tcp: i/o timeout

this happens every now and then but not for all requests, beacuse of this my application pods are failing.
What could be the possible reason for this behaviour??

now i faced this problem. How did you solve the problem? @Prashanth-M