Traefik not generating a certificate

Traefik Traefik v2 (latest)
1

I'm using the same configuration in two domains, both using cloudflare and dns authentication, yet one of them does not have a valid certificate.

Here's what the error log shows:

time="2020-03-23T08:54:51Z" level=info msg="Enabling ProxyProtocol for trusted IPs []" entryPointName=https
time="2020-03-23T08:54:51Z" level=info msg="Starting provider aggregator.ProviderAggregator {}"
time="2020-03-23T08:54:51Z" level=info msg="Starting provider *file.Provider {\"directory\":\"config/\",\"watch\":true}"
time="2020-03-23T08:54:52Z" level=info msg="Starting provider *docker.Provider {\"watch\":true,\"endpoint\":\"unix:///var/run/docker.sock\",\"defaultRule\":\"Host(`DOMAIN.TLD`) \\u0026\\u0026 PathPrefix(`/{{ trimSuffix \\\"-settings\\\" .Name }}`)\",\"exposedByDefault\":true,\"network\":\"traefik_proxy\",\"swarmModeRefreshSeconds\":15000000000}"
time="2020-03-23T08:54:52Z" level=info msg="Starting provider *acme.Provider {\"email\":\"johnny@brunoamaral.eu\",\"caServer\":\"https://acme-v02.api.letsencrypt.org/directory\",\"storage\":\"acme.json\",\"keyType\":\"RSA4096\",\"dnsChallenge\":{\"provider\":\"cloudflare\"},\"httpChallenge\":{\"entryPoint\":\"http\"},\"ResolverName\":\"default\",\"store\":{},\"ChallengeStore\":{}}"
time="2020-03-23T08:54:52Z" level=info msg="Testing certificate renew..." providerName=default.acme
time="2020-03-23T08:54:52Z" level=info msg="Starting provider *traefik.Provider {}"

The difference is that the first domain is configured in a file and the other through the docker-compose labels.

labels:
  - traefik.enable=true
  - "traefik.http.routers.heimdall.rule=Host(`${DOMAIN_NAME_2}`)||Host(`www.${DOMAIN_NAME_2}`)"
  - "traefik.http.routers.heimdall.tls=true"
  - "traefik.http.services.heimdall.loadbalancer.server.port=8000"

I'm at a loss here, any idea of what I am missing? Where should I go to further investigate?