This is the right place. However, this is weird. Nothing has changed those days. The link https://www.sslshopper.com/ssl-checker.html#hostname=www.plantuml.com
www.plantuml.com resolves to 22.214.171.124
The certificate was issued by GeoTrust. Write review of GeoTrust
The certificate will expire in 1048 days.
The hostname (www.plantuml.com) is correctly listed in the certificate.
The certificate is not trusted in all web browsers.
You may need to install an Intermediate/chain certificate to link it to a trusted root certificate. Learn more about this error.
You can fix this by following GeoTrust's Certificate Installation Instructions for your server platform (use these instructions for RapidSSL).
Pay attention to the parts about Intermediate certificates.
Common name: plantuml.com
SANs: plantuml.com, www.plantuml.com
Valid from May 13, 2017 to August 12, 2020
Serial Number: 0878320c3b90e1a0a7e8066a860387a8
Signature Algorithm: sha256WithRSAEncryption
Issuer: RapidSSL SHA256 CA
So it looks fine to us. Could you check again ? Thanks!