Invalid SSL certificate Error code 526 Problem only on one subdomain

[uokufa]

What is the name of the domain?

https://edu-girls.uokufa.edu.iq/

What is the error number?

526

What is the issue you’re encountering

I’m getting Invalid SSL certificate Error code 526 on one of our subdomains which was working fine 48 hours ago. I did research on this error which usually occurs when the certificate is invalid on the origin server however we have no issue with all of our subdomains (such as https://eng.uokufa.edu.iq) except for this particular subdomain. In other words the same certificate is validated by CF on all of our subdomains (including the main domain) with no issue except for that particular subdomain. Kindly note that I’m on Full Strict mode. Disabling CF or switching to Full mode fix the issue but I’d rather find the real cause of the problem. I contacted my host provider and they said that the certificate is valid and most likely the problem is with CF since the same certificate is validated by CF on the other subdomains.

Was the site working with SSL prior to adding it to Cloudflare?

Yes

What is the current SSL/TLS setting?

Full (strict)

[cscharff]

You don’t have a valid certificate on the origin server associated with that hostname for the subdomain in question. Have you actually checked the origin server specified in Cloudflare DNS yourself to determine the certificate is valid for that hostname?