Inquiry about grafana display issue

Dear team,

We are using PromQL probe_ssl_earliest_cert_expiry{c_http="$HTTPS"}-time()
To display the certification expiration status. But some urls can display number, but some cannot.

When we check the result in Prometheus, for example, https://chat.vwfs.com.cn, in Prometheus, it displays as bellow, and do have value, which cannopt display in Grafana dashboard:

Would you please help to advise what might be the root cause? Thank you.