Apparently the cert was missing on a fresh Windows 10 install I just did as well. While I did have the DigiCert Global Root CA, I was missing the AddTrust External CA Root. I downloaded the cert as follows
Download the “AddTrust External CA Root” certificate from https://support.cloudflare.com/hc/en-us/articles/115001186052-What-intermediates-and-roots-are-Cloudflare-issued-certs-signed-against- you’ll need the cert that has a serial number of 1 and has a SHA-1 Fingerprint ending in 1868
In Windows 10 you can just double click the cert and it will run a wizard to have you install it.
Once installed i did a reboot and like magic my posters are now loading for my shows.
